Methods to produce chimeric adeno-associated virus/bocavirus parvovirus

ABSTRACT

A method of preparing a chimeric virus comprising bocavirus capsid protein (VP) and a recombinant adeno-associated (AAV) viral genome, and isolated mutant bocavirus genomes, are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 16/076,219, filed on Aug. 7, 2018, which application is a U.S. National Stage Filing under 35 U.S.C. 371 from International Application No. PCT/US2017/017021, filed on Feb. 8, 2017, and published as WO 2017/139381 on Aug. 17, 2017, which application claims the benefit of the filing date of U.S. application Ser. No. 62/292,613, filed on Feb. 8, 2016 and U.S. application Ser. No. 62/453,745, filed on Feb. 2, 2017, the disclosures of which are incorporated by reference herein.

STATEMENT OF GOVERNMENT RIGHTS

This Invention was made with government support under grants AI105543 and AI112803 awarded by the National Institutes of Health. The Government has certain rights in the invention.

INCORPORATION BY REFERENCE OF SEQUENCE LISTING

A Sequence Listing is provided herewith as an xml file, “2332390.xml” created on May 8, 2023 and having a size of 14.065 bytes. The content of the xml file is incorporated by reference herein in its entirety.

BACKGROUND

Human bocavirus1 (HBoV1), first identified in 2005 (Aflander et al., 2005), belongs to genus Bocaparvovirus in the subfamily Parvovirinae of the Parvoviridae family (Cotmore et al., 2014). The genus Bocaparvovirus consists of three groups of viruses, namely HBoV1-4, bovine parvovirus 1 (BPV1) and minute virus of canines (MVC/CnMV) (Johnson and Qiu, 2011). HBoV1 causes respiratory tract infection in young children worldwide (Allander et al., 2007; Christensen et al., 2010; Deng et al., 2012; Don et al., 2010; Edner et al., 2011; Kantola et al., 2008; Martin et al., 2015). In vitro, the virus infects only polarized (well-differentiated) human airway epithelium cultured at an air-liquid interface (HAE-ALI) (Dijkman et al., 2009; Huang et al., 2012; Deng et al., 2013; Deng et al., 2014). An infectious clone of HBoV1 (pIHBoV1) was constructed. Transfecting the pIHBoV1 in human embryonic kidney 293 (HEK293) cells results in efficient replication of the HBoV1 genome and production of HBoV1 virions, which are infectious in HAE-ALI (Huang et al., Deng et al., 2013).

The transcription profile of HBoV1 has been studied in transfection of both HBoV1 non-replicating and replicating double-stranded DNA (dsDNA) forms of the viral genome in HEK293 cells (Chen et al., 2010; Shen et al., 2015), as well as during HBoV1 Infection of HAE-ALI (Dijkman et al., 2009; Shen et al., 2015). All the viral mRNA transcripts are generated from alternative processing (involving both splicing and polyadenylation) of one HBoV1 precursor-RNA (pre-mRNA), which is transcribed from the P5 promoter (FIG. 1A) (Dijkman et al., 2009; Chen et al., 2010; Shen et al., 2015). The left side of the genome encodes non-structural (NS) proteins, and four major NS proteins (NS1, NS2, NS3, and NS4) are expressed from alternatively spliced mRNA transcripts (Shen et al., 2015). While NS1 is critical to viral DNA replication, NS2 also plays a role during virus replication in infection of HAE-ALI (Shen et al., 2015). The right side of the genome encodes viral capsid proteins from alternatively spliced mRNA transcripts. R6, R7, and R8 mRNAs (FIG. 1A). Of note, HBoV1, like other members of the genus Bocaparvovirus, encodes a unique nonstructural protein NP1 from the middle of the genome. NP1 is required for an efficient replication of viral DNA (Huang et al., 2012; Sun et al., 2009).

HBoV1 capsid is capable of cross-genus packaging of a genome of recombinant adeno-associated virus 2 (rAAV2) in HEK293 cells, which generates HBoV1 capsid-pseudotyped 129 rAAV2 vector (rAAV2/HBoV1) (Yan et al., 2013). The chimeric vector can deliver a full-length cystic fibrosis transmembrane conductance regulator (CFTR) gene with a strong promoter to cystic fibrosis (CF) HAE, with demonstrated efficacy in correcting CFTR-dependent chloride transport (Yan et al., 2013). Therefore, the rAAV2/HBoV1-CFTR vector holds much promise for CF gene therapy. However, in the current vector production system, the packaging plasmid pHBoV1NSCap, which carries an HBoV1 non-replicating dsDNA genome (containing the P5 promotor and NS and Cap genes), was used for packaging rAAV2/HBoV1 vector. The efficiency of the vector production is on average 10 times lower than that of the rAAV2 vector packaged by the AAV2 capsid (Yan et al., 2013). It was hypothesized that this lower efficiency is likely due to the unnecessary expression of the HBoV1 NS gene from the packaging plasmid pHBoV1NSCap.

SUMMARY

Chimeric parvovirus vector rAAV/HBoV inherits the safety of rAAV (recombinant adeno-associated virus) and the airway tropism of HBoV (human bocavirus type 1), which provides a solution for the current lack of an efficient vector for airway gene therapy of pulmonary diseases, such as cystic fibrosis, alpha-antitrypsin deficiency, asthma, vaccines, and lung cancer.

This disclosure provides improved methods to produce chimeric AAV/BoV viruses, e.g., using a chimeric parvoviral vector (rAAV2/HBoV1) vector, in which the recombinant adeno-associated virus (rAAV) genome is pseudo-packaged by the human bocavirus 1 (HBoV1) capsid, such as one expressing a full-length cystic fibrosis transmembrane conductance regulator (CFTR) gene that is capable of correcting CFTR81 dependent chloride transport in cystic fibrosis human airway epithelium. Previously, an HBoV1 nonstructural (NS) and capsid (Cap) protein-expressing plasmid, pHBoV1NSCap, was used to package a rAAV2/HBoV1 vector, but yields remain low, e.g., 2×10¹¹ DNAase-resistant particles (DRPs)/40 150 mm dishes of transfected cells (400-600 DRP/cell), which is about 5% to about 10% the typical yield of rAAV2 production). In order to simplify this packaging plasmid, the involvement of the HBoV1 nonstructural proteins in capsid protein expression was investigated as described below. It was found that NP1, a small NS protein encoded by the middle open reading frame, allows for the expression of the viral capsid proteins (VP1, VP2, and VP3), whereas the other NS proteins (NS1, NS2, NS3, and NS4) are not necessarily required. Systematic analyses of the HBoV1 mRNAs transcribed from the pHBoV1NSCap packaging plasmid and its derivatives in HEK293 cells were performed. By mutating the cis-elements, which function as internal polyadenylation signals in the capsid protein-expressing mRNA, a simple HBoV1 capsid protein gene was constructed that expresses capsid proteins VP1, VP2 and VP3 as efficiently as pHBoV1NSCap and at similar ratios, but independently of the NP1. Thus, mechanistically, it was found that NP1 is required for both the splicing and the read-through of the proximal polyadenylation site of the HBoV1 precursor-mRNA, both of which are essential for the maturation of capsid protein-encoding mRNA. Thus, the present disclosure provides a unique example of how a small viral nonstructural protein facilitates the multifaceted regulation of capsid gene expression. Moreover, a function of HBoV1 NP1 in the regulation of capsid protein expression was identified, which allows for a better packaging system for rAAV/HBoV vector production.

The present invention provides a method of preparing a chimeric virus comprising bocavirus capsid protein (VP) and a recombinant adeno-associated (AAV) viral genome. Any AAV genome may be employed, e.g., any mammalian AAV including any primate AAV, a human or non-human primate AAV, including a chimeric AAV genome such as one having synthetic or chimeric ITRs (see, e.g., U.S. Pat. No. 8,241,622, which is incorporated by reference herein), or formed from AAV DNA from two or more different serotypes, e.g., a chimeric genome having 2 ITRs, each ITR from a different serotype or chimeric ITRs. Any bocavirus or bocavirus genome may be employed in the methods, for example, a human bocavirus or human bocavirus genome. In one embodiment, the method is NP1 dependent, and according to one embodiment, the method comprises providing a mutant bocavirus, e.g., HoBV1, genome that when introduced into cells: i) does not express one or more of NS1, NS2, NS3 or NS4; for example, expresses none of NS1, NS2, NS3, NS4; or expresses only NS1 or NS2 or NS3 or NS4; or expresses any two of NS1, NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3, NS4, for example, expresses NS2, NS3 and NS4, ii) expresses one or more of bocavirus VP1, VP2 or VP3, for example, expresses VP1 and VP2 and VP3, or expresses VP1 and VP2, or expresses VP1 and VP3, or expresses VP2 and VP3, and ii) expresses bocavirus NP1. The method can further include introducing the mutant bocavirus genome and a rAAV vector into cells which do not express one or more of bocavirus NS1, NS2, NS3 or NS4, as defined above thereby producing bocavirus VP, bocavirus NP1 and a rAAV genome; and can further comprise collecting chimeric rAAV/bocavirus. Optionally the collecting of chimeric rAAV/bocavirus can be from the cells or the cell supernatant, for example, where the cells are grown in culture medium.

According to one embodiment the method comprises providing one or more vectors that express one or more of bocavirus VP1, VP2 or VP3; for example, express VP1 and VP2 and VP3, or express VP1 and VP2, or express VP1 and VP3, or express VP2 and VP3, and express bocavirus NP1 but do not express one or more of bocavirus NS1, NS2, NS3 or NS4, for example, expresses none of NS1, NS2, NS3, NS4, or expresses only NS1 or NS2 or NS3 or NS 4; or expresses any two of NS1, NS2, NS3. NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3. NS4, for example, expresses NS2, NS3 and NS4. The method can further comprise expressing the one or more vectors in cells which do not express one or more of bocavirus NS1, NS2, NS3 or NS4, as defined above thereby producing bocavirus VP, bocavirus NP1 and a rAAV genome; and can further comprise collecting chimeric rAAV/bocavirus, optionally the collecting chimeric rAAV/bocavirus can be from the cells or the cell supernatant, for example, where the cells are grown in culture medium The one or more vectors may be integrated into the genome of the cells. The bocavirus can be a human bocavirus or the genome a human bocavirus genome.

According to the invention, the mutant bocavirus genome and a rAAV vector can be introduced into cells thereby producing bocavirus capsid protein (VP) and bocavirus NP1, and a rAAV genome. A mutant BoV genome, e.g., a mutant human BoV genome or a non-human BoV genome, may include one or more insertions, one or more deletions, or one or more nucleotide substitutions, e.g., substitutions that results in an in-frame stop codon or removal of a splice site, or any combination thereof, in order to inhibit or prevent expression of a functional viral protein. The chimeric rAAV/bocavirus virus can then be collected, optionally the collecting chimeric rAAV/bocavirus can be from the cells or the cell supernatant, for example, where the cells are grown in culture medium. According to the invention, the one or more vectors may be integrated into the genome of the cells. According to the invention the bocavirus may be a human bocavirus or the genome may be a human bocavirus genome.

In one embodiment, the rAAV vector comprises an expression cassette encoding a heterologous gene product. In one embodiment, the gene product encodes a therapeutic protein. In one embodiment, the rAAV genome is a rAAV-1, rAAV-2, rAAV-3, rAAV-4, rAAV-5, rAAV-6, rAAV-7, rAAV-8 or rAAV-9 genome. In one embodiment, the gene product is a viral, bacterial, tumor, parasite, or fungal antigen. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator, C1 inhibitor gene, C1-INH gene, SERPING gene, β-globin, γ-globin, tyrosine hydroxylase, glucocerebrosidase, aryl sulfatase A, factor VIII, dystrophin, alpha 1-antitrypsin, surfactant protein SP-D, SP-A or SP-C, erythropoietin, HBoV protein, influenza virus protein, RSV protein, a neutralizing antibody or an antigen binding fragment thereof, SARS virus protein, or a cytokine, e.g., IFN-alpha, IFN-gamma, TNF, IL-1, IL-17, or IL-6. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator. In one embodiment, the gene product is C1 inhibitor gene, C1-INH gene, or SERPING1 gene. In one embodiment, the DNAase-resistant particles. DRPs, of the chimeric virus which are produced are at least about 5% greater than the DRPs produced of a corresponding chimeric virus where the bocavirus genome also expresses bocavirus NS protein, for example, that expresses all of NS1, NS2, NS3. NS4, or that expresses one or more of NS1, NS2, NS3 or NS4, or that expresses the one or more of NS1, NS2, NS3 or NS4 not expressed by the chimeric virus produced by the methods described herein. In one embodiment, the yield is about 1,000 to about 10,000 DRP/cell, e.g., about 1,500 to about 6,000 DRP/cell. The AAV genome may be stably incorporated Into the genome of the cell, e.g., via homologous recombination or random integration.

Also provided is a method of preparing a chimeric virus comprising bocavirus capsid protein and a recombinant adeno-associated (AAV) viral genome, which method is NP1 dependent. The method comprises providing one or more vectors that express one or more of VP1, VP2 or VP3, for example, express VP1 and VP2 and VP3, or express VP1 and VP2, or express VP1 and VP3, or express VP2 and VP3, and express NP1 but do not express one or more of NS1, NS2, NS3 or NS4, for example, expresses none of NS1, NS2, NS3, NS4; or expresses only NS1 or NS2 or NS3 or NS 4; or expresses any two of NS1, NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3. NS4, for example, expresses NS2, NS3 and NS4; expressing the vectors in cells; optionally wherein the cells do not express one or more of bocavirus NS1, NS2, NS3 or NS4, as defined above, and collecting chimeric virus. Optionally the collecting of chimeric virus can be from the cells or the cell supernatant, for example, where the cells are grown in culture medium. In one embodiment, the rAAV vector comprises an expression cassette encoding a heterologous gene product. In one embodiment, the gene product encodes a therapeutic protein. In one embodiment, the rAAV genome is a rAAV-1, rAAV-2, rAAV-3, rAAV-4, rAAV-5, rAAV-6, rAAV-7, rAAV-8 or rAAV-9 genome. In one embodiment, the gene product is a viral, bacterial, tumor, parasite, or fungal antigen. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator, C1 Inhibitor gene, C1-INH gene, SERPING1 gene, β-globin, γ-globin, tyrosine hydroxylase, glucocerebrosidase, aryl sulfatase A, factor VIII, dystrophin, alpha 1-antitrypsin, surfactant protein SP-D, SP-A or SP-C, erythropoietin, HBoV protein, influenza virus protein, RSV protein, a neutralizing antibody or an antigen binding fragment thereof, SARS virus protein, or a cytokine, e.g., IFN-alpha, IFN-gamma, TNF, IL-1, IL-17, or IL-6. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator. In one embodiment, the gene product is C1 Inhibitor gene, C1-INH gene, or SERPING1 gene. In one embodiment, DRP of the chimeric virus is at least about 5% greater than a corresponding chimeric virus where the bocavirus genome also expresses bocavirus NS protein, for example that expresses all of NS1, NS2, NS3, NS4, that also expresses one or more of NS1, NS2, NS3 or NS4, or that expresses the one or more of NS1, NS2, NS3 or NS4 not expressed by the chimeric virus of the invention.

Further provided is a method of preparing a chimeric virus comprising bocavirus capsid protein and a recombinant adeno-associated (AAV) viral genome, which method is independent of bocavirus NP1. In one embodiment, the method comprises providing a mutant bocavirus genome that when introduced into cells expresses one or more of bocavirus NS1, NS2, NS3 or NS4, for example, that expresses only NS1 or NS2 or NS3 or NS4; or expresses any two of NS1, NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3, NS4, for example, expresses NS2, NS3 and NS4, or that expresses all of NS1, NS2, NS3, NS4; or alternatively expresses none of NS1, NS2, NS3, NS4, expresses one or more of bocavirus VP1, VP2 or VP3, for example, expresses VP1 and VP2 and VP3, or expresses VP1 and VP2, or expresses VP1 and VP3, or expresses VP2 and VP3, but does not express bocavirus NP1 or a functional bocavirus NP1, wherein optionally the coding region for the one or more of the VP1, VP2 or VP3 is codon optimized (SEQ ID Nos. 2-3). In one embodiment, the mutant genome expresses VP1, VP2 and VP3. In one embodiment, the method includes providing a mutant bocavirus genome that when introduced into cells does not express any of bocavirus NS1, NS2, NS3 or NS4, expresses one or more of bocavirus VP1, VP2 or VP3, for example, expresses VP1 and VP2 and VP3, or expresses VP1 and VP2, or expresses VP1 and VP3, or expresses VP2 and VP3, but does not express bocavirus NP1 or a functional bocavirus NP1, wherein optionally the coding region for the one or more of the VP1, VP2 or VP3 is codon optimized (SEQ ID Nos. 2-3). In one embodiment, the method includes providing one or more vectors that when introduced to cells express one or more of bocavirus VP1, VP2 or VP3, but do not express bocavirus NP1 or a functional bocavirus NP1 or any of NS1, NS2, NS3 or NS4, wherein optionally the coding region for the one or more of the VP1, VP2 or VP3 is codon optimized (SEQ ID Nos. 2-3). Optionally or additionally, the mutant genome and a rAAV vector are introduced into cells that do not express NP1 in trans, for example, the method can further comprise introducing the mutant bocavirus genome and a rAAV vector into cells that do not express bocavirus NP1 in trans, thereby producing bocavirus nonstructural proteins NS1, NS2, NS3 or NS4, capsid proteins and a rAAV genome. The method can further comprise collecting the chimeric virus or chimeric rAAV/bocavirus, and optionally the collecting can be from the cells or the cell supernatant, for example, where the cells are grown in culture medium. In one embodiment, the promoter that expresses bocavirus proteins is not a bocavirus promoter, e.g., not a HBoV promoter. The bocavirus can be human bocavirus. In one embodiment, the rAAV vector comprises an expression cassette encoding a heterologous gene product. In one embodiment, the rAAV genome is a rAAV-1, rAAV-2, rAAV-3, rAAV-4, rAAV-5, rAAV-6, rAAV-7, rAAV-8 or rAAV-9 genome wherein the gene product encodes a therapeutic protein. In one embodiment, the gene product is a viral, bacterial, tumor, parasite, or fungal antigen. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator, C1 Inhibitor gene, C1-INH gene, SERPING1 gene, β-globin, γ-globin, tyrosine hydroxylase, glucocerebrosidase, aryl sulfatase A, factor VIII, dystrophin, alpha 1-antitrypsin, surfactant protein SP-D, SP-A or SP-C, erythropoietin, HBoV protein, influenza virus protein, RSV protein, a neutralizing antibody or an antigen binding fragment thereof, SARS virus protein, or a cytokine, e.g., IFN-alpha, IFN-gamma, TNF, IL-1, IL-17, or IL-6. In one embodiment, the gene product is cystic fibrosis transmembrane conductance regulator. In one embodiment, the gene product is C1 inhibitor gene, C1-INH gene, or SERPING1 gene. In one embodiment, the DRP of the chimeric virus is at least about 5% greater than a corresponding chimeric virus with a bocavirus genome that also expresses bocavirus NS protein, for example that expresses all of NS1, NS2, NS3 NS4, that also expresses one or more of NS1, NS2, NS3 or NS4, or that expresses the one or more of NS1, NS2, NS3 or NS4 not expressed by the chimeric virus of the invention. According to one embodiment of the method of the invention neither the cells nor the mutant genome provides for expression of any of bocavirus NS1, NS2, NS3 or NS4.

In one embodiment, the invention also provides a method of preparing a chimeric virus comprising bocavirus capsid protein and a recombinant adeno-associated (AAV) viral genome which method is independent of bocavirus NP1. In one embodiment, the method comprises providing one or more vectors that when introduced to cells express one or more of NS1, NS2, NS3 or NS4, for example, that expresses only NS1 or NS2 or NS3 or NS 4; or expresses any two of NS1, NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3, NS4, for example, expresses NS2, NS3 and NS4, or that expresses all of NS1, NS2, NS3, NS4, or alternatively do not express any of NS1, NS2, NS3, NS4; express one or more of bocavirus VP1, VP2 or VP3, for example, express VP1 and VP2 and VP3, or express VP1 and VP2, or express VP1 and VP3, or express VP2 and VP3, but do not express bocavirus NP1 or a functional bocavirus NP1, wherein the coding region for the one or more of the bocavirus VP1, VP2 or VP3 may be codon optimized. In one embodiment, the method includes providing one or more vectors that when introduced to cells express one or more of bocavirus VP1, VP2 or VP3, but do not express bocavirus NP1 or a functional bocavirus NP1 or any of NS1, NS2, NS3 or NS4. In one embodiment, the one or more vectors express VP1, VP2 and VP3. In one embodiment, the coding region for the one or more of the bocavirus VP1, VP2 or VP3 is codon optimized. Those vectors and a rAAV vector are expressed in cells that do not express NP1 in trans thereby, producing bocavirus capsid protein and a rAAV genome; and chimeric virus is collected. For example the method can further comprise expressing the one or more vectors and a rAAV vector in cells that do not express NP1 in trans, thereby producing bocavirus nonstructural proteins NS1, NS2. NS3 or NS4 capsid protein and a rAAV genome; and collecting chimeric rAAV/bocavirus, optionally the collecting chimeric virus can be collecting from the cells or the cell supernatant, for example where the cells are grown in culture medium. The method can further comprise that the one or more vectors are integrated into the genome of the cell and can additionally or alternatively comprise that neither the cells nor the one or more vectors provides for expression of any of bocavirus NS1, NS2, NS3 or NS4.

According to some embodiments of the invention, the promoter that expresses bocavirus proteins is not a bocavirus promoter.

According to a further aspect of the invention there is provided an isolated mutant bocavirus genome that when introduced to cells does not express one or more of bocavirus NS1, NS2, NS3 or NS4, for example, expresses none of NS1, NS2, NS3, NS4; or expresses only NS1 or NS2 or NS3 or NS 4; or expresses any two of NS1, NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3, NS4, for example, expresses NS2, NS3 and NS4; expresses bocavirus VP1, VP2 and VP3; and expresses bocavirus NP1. Optionally the promoter that expresses bocavirus proteins is not a bocavirus promoter.

According to a further aspect of the invention there is provided an isolated mutant bocavirus genome that when introduced to cells i) expresses one or more of bocavirus NS1, NS2, NS3 or NS4, for example, that expresses only NS1 or NS2 or NS3 or NS 4; or expresses any two of NS1. NS2, NS3, NS4, for example, expresses NS3 and NS4; or expresses any three of NS1, NS2, NS3. NS4, for example, expresses NS2, NS3 and NS4, or that expresses all of NS1, NS2, NS3, NS4, ii) expresses bocavirus VP1, VP2 and VP3; and iii) does not express bocavirus NP1 or a functional bocavirus NP1. Optionally the promoter that expresses bocavirus proteins is not a bocavirus promoter.

According to a further aspect of the invention there is provided an isolated mutant bocavirus genome that when introduced to cells i) does not express any of bocavirus NS1, NS2, NS3 or NS4; ii) expresses bocavirus VP1, VP2 and VP3; and iii) does not express bocavirus NP1 or a functional bocavirus NP1. Optionally the promoter that expresses bocavirus proteins is not a bocavirus promoter.

According to a further aspect of the invention there is provided an isolated mutant bocavirus genome and bocavirus protein expression vector(s). A mutant BoV genome, e.g., a mutant human BoV genome or a non-human BoV genome, may include one or more insertions, one or more deletions, or one or more nucleotide substitutions, e.g., substitutions that results in an in-frame stop codon or removal of a splice site, or any combination thereof, in order to inhibit or prevent expression of a functional viral protein. In one embodiment, there is provided an expression vector comprising a codon optimized open reading frame for bocavirus NP1, or bocavirus VP1. VP2 or VP3, or a portion thereof. The open reading frame for NP1 can encode a protein with at least 80%, 85%, 90%, 95%, 98% or more identity to the protein encoded by SEQ ID NO:1, that is, NP1 useful in the methods may be a protein with at least 80%, 85%, 90%, 95%, 98% or more identity to the protein encoded by SEQ ID NO:1. The open reading frame for bocavirus VP1, VP2 and VP3 can encode proteins with at least 80%, 85%, 90%, 95%, 98% or more identity to the protein encoded by any one of SEQ ID Nos. 2-3, e.g., bocavirus VP1, VP2 and VP3 useful in the methods may be a protein with at least 80%, 85%, 90%, 95%, 98% or more identity to the protein encoded by any one of SEQ ID Nos. 2-3. Coding regions for NP1 and capsid proteins from AAVs, e.g., other than AAV2, may likewise by codon optimized. According to one embodiment the expression vector comprises a heterologous promoter linked to the open reading frame.

BRIEF DESCRIPTION OF FIGURES

FIGS. 1A-C. Genetic map of HBoV1 and the probes used. A-B) The expression profile of HBoV1 mRNAs and their encoded proteins are shown with transcription landmarks and boxed open reading frames (ORFs). The numbers are nucleotide (nt) numbers of the HBoV1 full-length genome (GenBank accession no.: JQ923422). Major species of HBoV1 mRNA transcripts that are alternatively processed are shown with their sizes in kilobases (kb) (minus a poly A tail of about 150 nts), which were concluded from multiple studies in HBoV1 DNA transfection of HEK293 cells and in HBoV1 infection of polarized human airway epithelium (Dijkman et al., 2009; Chen et al., 2010; Shen et al., 2015). Viral proteins detected in both transfected and infected cells are shown side by side at the right. P5, P5 promoter; D, 5′ splice donor site; A, 3′ splice acceptor site; (pA)p and (pA)d, proximal and distal polyadenylation sites, respectively; LEH/REH, left/right end hairpin. C) Probes used for Northern blot analysis are depicted with the nucleotide numbers. Probes used for RNAse protection assay (RPA) are diagrammed with the sizes of their detected bands.

FIG. 2 . DNA sequence of silent mutations in the (pA)p sites (SEQ ID NO:5). Nucleotide sequences between the VP1 and VP3 start codons were silently mutated to eliminate potentially used (cryptic) polyadenylation signals (PAS: AAUAAA), but still retain the same coding sequence as the wild type. The mutated sequence is shown with locations of the 5 PASs (dashed underline). The VP1 start codon was mutated from ATG to ACG, together with a weak Kozak signal (GTT AAG), and retained VP2 start codon GTG.

FIGS. 3A-B. VP2 is translated from a non-canonical translation initiation codon. A) Diagrams of pHBoV1NSCap-based mutants. The parent pHBoV1NSCap plasmid is diagrammed with transcription, splicing, and polyadenylation units shown, together with the mutants that carry various mutations at the GUG and GCU codons (nt 3,422-3,427) of the HBoV1 genome, as shown. B) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. The lysates of transfected cells were analyzed by Western blotting using an anti-VP antibody, and was reprobed with anti-β-actin. The Identities of the detected bands are indicated at the left of the blot. Arrow shows the novel VP2 protein, which was denoted previously by an asterisk (*) (Shen et al., 2015). Control, without transfection.

FIGS. 4A-D. HBoV1 VP cDNA constructs did not express capsid proteins. A) Diagrams of HBoV1 VP cDNA constructs, pHBoV1NSCap is diagramed with transcription, splicing, and polyadenylation units shown, pCMVCap1-3 and pCMVR6-8cDNA that contain various sequences of the 5′ untranslational region (UTR) and 3′UTR and the VP1/2/3 ORF are diagramed with the junction of the 5′ and 3′ splice sites or the heterogeneous Epo intron 4 (Epo In4) as shown. B) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. The lysates of transfected cells were analyzed by Western blotting using an anti-VP antibody, and were reprobed with anti-β-actin. The lysates were also analyzed by Western blotting using an anti-HA antibody for detecting the C-terminal HA-tagged mCherry. The identities of the detected bands are indicated at the left of the blot. C) Northern blot analysis of cytoplasmic VP mRNAs. HEK293 cells were transfected with plasmids as indicated. Cytoplasmic RNA prepared from each transfection was analyzed by Northern blotting using the Cap probe, which specifically detects VP mRNA (FIG. 1B). EB stained 18S rRNA bands are shown, and the VP mRNA bands are indicated. Asterisk (*) denotes various NS-encoding mRNAs. A RNA ladder (M) was used as a size marker. D) Quantification of VP mRNA expression. The bands of VP mRNA in each lane of panel C were quantified and normalized to the level of 18S rRNA. The signal intensity of the VP mRNA band in lane 1 was arbitrally set as 100%. Relative intensity was calculated for the bands in other lanes. Means and standard deviations were calculated from at least three independent experiments.

FIGS. 5A-D. Knockout of NP1 abolished VP mRNA production and capsid protein expression. A) Diagrams of HBoV1 NSCap gene constructs. pHBoV1NSCap and its derivatives are diagramed with replacement of the CMV promoter and bGHpA signal and knockout of the NS1 and NP1 as shown. B) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. Cell lysates were analyzed by Western blotting using an anti-VP antibody. The blot was reprobed with anti-β-actin. The lysates were also analyzed by Western blotting using anti-NP1 and anti-HA antibodies. The identities of detected proteins are shown at the left of the blot. C) Northern blot analysis of cytoplasmic VP mRNAs. HEK293 cells were transfected with plasmids as indicated. Cells were harvested and extracted for cytoplasmic RNA at 2 days post-transfection. The cytoplasmic RNA samples were analyzed by Northern blotting using the Cap probe. EB-stained 18S rRNA and detected VP mRNA are indicated. Asterisk (*) denotes various NS-encoding mRNAs. D) Western blot analysis of NS proteins. The same lysates prepared for panel B were analyzed by Western blotting using an anti-NS1C antibody. The identities of detected proteins are shown at the left of the blot.

FIGS. 6A-H. NP1 complementation rescued VP mRNA production and capsid proteins expression. A) Diagrams of HBoV1 NSCap constructs. pCMVNS*Cap and pCMVNS*(NP*)Cap are diagrammed, along with the pOpt-NP1 plasmid that expresses NP1 from a codon-optimized NP1 ORF (SEQ ID NO:1). (B) RPA analysis of viral RNAs spliced at the A1, D2 and A3 splice sites. Ten μg of total RNA isolated at 2 days post-transfection from HEK293 cells transfected with plasmids as indicated, was protected by both the pA1D2 and pA3 probes. Lane M. 32P-labeled RNA markers (Qiu et al., 2002), with sizes indicated to the left. The origins of the protected bands in the lanes are indicated to the left and right for pA1D2 and pA3 probes, respectively. Spl, spliced RNAs; Unspl, unspliced RNAs. C) Quantification of the mRNAs spliced at the A3 splice acceptor. The bands of both spliced and unspliced RNAs in lanes 4-6 of panel B were quantified. The ratio of spliced vs. unspliced RNA (A3 Spl/Unspl) was calculated and is shown with means and standard deviations from three independent experiments. Numbers shown are P values calculated using a two-tailed Student's t test. D) Northern blot analysis of cytoplasmic VP mRNAs. HEK293 cells were transfected with plasmids as indicated, and were harvested at two days post-transfection. Cytoplasmic RNA was extracted, and the RNA samples were analyzed by Northern blotting using the Cap probe. EB-stained 18S rRNA and VP mRNA are indicated. Asterisk (*) denotes various NS-encoding mRNAs. E) Western blot analysis of capsid proteins. Transfected cells were harvested and lysed at 2 days post-transfection. The lysates were analyzed by Western blotting using an anti-VP antibody. The blot was reprobed with anti-β-actin. The lysates were also analyzed by Western blotting using anti-NP1 and anti-HA antibodies. The identities of detected proteins are shown at the left of the blot. F)-H) VP mRNA was exported from the nucleus to cytoplasm efficiently and was stable. F) Northern blot analysis. HEK293 cells were transfected with plasmids as indicated with or without co-transfection of the pOpt-NP1. The same numbers of cells were harvested and extracted for both total and cytoplasmic RNA. RNA samples were analyzed by Northern blotting using the Cap probe. EB-stained 18S rRNA and VP mRNA are indicated. Asterisk (*) denotes various NS617 encoding mRNAs. G) Quantification of VP mRNAs on Northern blots. The bands of VP mRNA in each lane of panel F were quantified and normalized to the level of 18S rRNA. The intensity of the VP mRNA band in lane 1 was arbitrally set as 100%. Relative VP mRNA level was calculated for the bands in other lanes. Means and standard deviations are quantified from three independent experiments. P values shown are calculated using a two-tailed Student's t-test. ND, not detectable. (H) RNA stability assay. HEK293 cells were transfected with pCMVNS*Cap. At 2 days post-infection, cells were treated with actinomycin D at 5 μg/mL for hours (hrs p.t.) as indicated. The treated cells were harvested and extracted for total RNA. The RNA samples were analyzed by Northern blotting using the NSCap probe (FIG. 1B). EB-stained 18S rRNA bands are shown. Indicated bands are detected VP mRNA at about 2.5 kb, which is likely the R6 mRNA that is polyadenylated at the (pA)d site, and (pA)p mRNA at about 1.5 kb, which is the R5s mRNA that is polyadenylated at the (pA)p site (FIG. 1A). Asterisk (*) denotes various NS-encoding mRNAs. Control, total RNA of non-transfected cells.

FIGS. 7A-E. NP1 increased VP mRNA production independent of RNA splicing at the A3 splice acceptor. A) Diagrams of HBoV1 Intron deletion/exchange constructs. Plasmids pCMVNS*(In3Δ)Cap, pCMVEpoIn14(In3Δ)Cap and pCMVEpoIn124Cap are diagrammed with replaced introns shown. B) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. Cells were harvested and lysed at 2 days post-transfection. The lysates were analyzed by Western blotting using an anti-VP antibody and reprobed with anti-β-actin. The lysates were also analyzed by Western blotting using anti-NP1 and anti-HA antibodies. C) Northern blot analysis of VP mRNAs. HEK293 cells were transfected with plasmids as indicated. Cells were harvested and extracted for total RNA at 2 days post-transfection. The total RNA samples were analyzed by Northern blotting using the NSCap probe. EB-stained 18S rRNA bands are shown. Detected bands of VP mRNA and (pA)p mRNA are indicated. Asterisk (*) denotes various NS-encoding mRNAs. Lane M, an RNA ladder marker. D) Quantification of VP mRNAs on Northern blots. The bands of VP mRNA and (pA)p mRNA in each lane of panel C were quantified and normalized to the level of 18S rRNA, respectively. The intensity of the VP mRNA band in lane 4 was arbitrally set as 100%. Relative intensities were calculated for the bands in other lanes. Means and standard deviations are calculated from three independent experiments. P values shown are calculated using a two-tiled Student's t test. Asterisks (*) denote P<0.01. E) Determination of the usage of the A1, D2, and A3 splice sites using RPA. Ten μg of total RNA isolated at two days post-transfection from HEK293 cells transfected with plasmids as indicated, was protected by the pA1D2 and pA3 probes or their homology counterparts, as indicated. Lane M. 32P-labeled RNA markers (Qiu et al., 2002), with sizes indicated to the left. The origins of the protected bands are shown with sizes. Spl, spliced RNAs; Unspl, unspliced RNAs.

FIGS. 8A-D. NP1 increased VP mRNA production from cDNA constructs. A) Diagrams of HBoV1 cDNA constructs. HBoV1 cDNA constructs are diagrammed along with the pCMVNS*(NP*)Cap control. B) Northern blot analysis of VP and (pA)p mRNAs. HEK293 cells were transfected with plasmids as indicated. Cells were harvested and extracted for total RNA at 2 days post-transfection. The RNA samples were analyzed by Northern blotting using the NSCap probe. EB-stained 18S rRNA bands of each sample are shown. The identities of detected bands are indicated. Asterisk (*) denotes various NS-encoding mRNAs. C) Quantification of VP and (pA)p mRNAs on Northern blots. The bands of VP mRNA and (pA)p mRNA in each lane of panel B were quantified and normalized to the level of 18S rRNA. The intensity of the VP mRNA band in lane 8 was arbitrally set as 100%. Relative intensity was calculated for the bands in other lanes. Means and standard deviations are calculated from three independent experiments. P values shown are calculated using a two-tailed Student's t test. Asterisks (**) indicate P<0.01. ND, not detectable. D) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. Cells were harvested and lysed at 2 days post-transfection. The lysates were analyzed by Western blotting using an anti-VP antibody. The blot was reprobed using an anti-β-actin antibody. The lysates were also analyzed by Western blotting using an anti-HA antibody.

FIGS. 9A-D. Mutation of the (pA)p sites enables VP mRNA production and capsid protein expression in the absence of NP1. A) Diagrams of HBoV1 NSCap and cDNA constructs. HBoV1 NS and Cap genes and cDNA constructs are diagrammed along with the pCMVNS*(NP*)Cap control. B) Northern blot analysis of VP and (pA)p mRNAs. HEK293 cells were transfected with plasmids as indicated. The total RNA samples were analyzed by Northern blotting using the NSCap probe. EB-stained 18S rRNA bands are shown. Detected bands of VP and (pA)p mRNAs are indicated to the left of the blot. Asterisk (*) denotes various NS-encoding mRNAs. C) Quantification of VP and (pA)p mRNAs on Northern blots. The bands of VP and (pA)p mRNAs in each lane in panel B were quantified and normalized to 18S rRNA. The intensity of the VP mRNA band in lane 1 was arbitrally set as 100%. Relative intensity was calculated for the bands of both VP and (pA)p mRNAs in other lanes. Means and standard deviations are calculated from three independent experiments. P values shown are calculated using a two-tailed Student's t test. Asterisks (**) indicate P<0.01. D) Western blot analysis of capsid proteins. HEK293 cells were transfected with plasmids as indicated. Cell lysates of each transfection were analyzed by Western blotting using an anti-VP antibody. The blot was reprobed with an anti-β-actin antibody. The lysates were also analyzed by Western blotting using an anti-HA antibody for mCherry expression.

FIGS. 10A-C. Both purified wild type HBoV1 virions and purified rAAV2/HBoV1 vectors do not contain any nonstructural proteins (NS1, NS2, NS2, NS4 and NP1). 8×10⁹ DPR (DNAse I digestion resistant particles) of wild type of HBoV1 (HBoV1) and rAAV2/HBoV1 vector rAAV2/HBoV1), which were purified by CsCl density-gradient centrifugation, were lyzed and separated on SDS-10% PAGE. After transferring, the blots were probed using anti-HBoV1 VP (Panel A) and anti-NS1 C-terminus (Panel B), respectively. The blot shown in panel B was reprobed with anti-HBoV1 NP1 (Panel C). An amount of 0.5 million of 293 cells transfected with pHBV1NSCap plasmid (pHBoV1NSCap) or not transfected (Control) were lyzed and analyzed as positive and negative controls, respectively. The identity of each band detected is indicated to the right side of the blots. A lane with protein markers is shown with their respective sizes to the left side of the blot. Asterisk indicates non-specific bands.

FIG. 11 . HBoV1 Genome Structure and Elements Used in rAAV/HBoV1 Helpers. LEH and REH represent the left and right end hairpin sequence at the termini of HBoV1 genome (GeneBank Accession no: JQ923422, which is incorporated by reference herein). NS1, NS2. NS3, NS4, NP1 are the non-structural protein; VP1, VP2 and VP3 are the capsid protein. All the HBoV1 encoded viral proteins are processed from a single preRNA transcribed from P5 promoter. (pA)p and (pA)d indicated the proximal and distal polyadenylation sites, respectively. NP1 plays a role for VP encoded mRNA splicing and read through the (pA)p sides. LEH and REH deleted HBoV1 genome is used as the prototype packaging helper, pHBoVNScap for rAAV2/HBoV1 vector production. Sites to be mutated to in-frame stop codon for early termination of the non-structural protein expression are marked in red. Mutation at the D1′ splicing donor prevents NP1 expression. Codon optimization of the HBoV1 capsid protein reading frame removes the five (pA)p sides in the unique region of the 5′ end of VP1 and VP2. OptVP1 or OptVP1U indicate regions of codon optimization of the full capsid coding sequence or only at the VP1/2 5′ unique region. An optimized Kozak sequence (GTT AAG ACG) is used in optVP1 and optVP1U to express VP1, and with the GUG codon for VP2 remaining intact, in order to obtain an appropriate ratio of the VP1:VP2:VP3.

FIGS. 12A-D. Optimized Sequences. A) Optimized NP1 sequence (SEQ ID NO:1). B) Optimized VP sequence (SEQ ID NO:2). Translation starts at an alternative start codon ACG of VP1, GTG for VP2, and ATG for VP3 (solid line box). VP1-3 are encoded in the same OFR; the short dashed line box shows the unique region of VP1, the long dashed line box shows the unique region of VP2. Bold: VP2; bold and underlined: VP3. Upper Cases: codon optimized. C) Optimized VP sequence (SEQ ID NO:3). Translation starts at an alternative start codon ACG of VP1, GTG for VP2, and ATG for VP3 (solid line box). VP1-3 are encoded in the same OFR: the short dashed line box shows the unique region of VP1, the long dashed line box shows the unique region of VP2. Bold: VP2; bold and underlined: VP3. Upper Cases: codon optimized, lower cases: original coding sequence in the HBoV1 genome. D) Exemplary wild-type VP sequence (SEQ ID NO:4). Translation starts at ATG for VP1, an alternative start codon GTG for VP2, and ATG for VP3 (solid line box). VP1-3 are encoded in the same OFR; the short dashed line box shows the unique region of VP1, the long dashed line box shows the unique region of VP2. Bold: VP2; bold and underlined: VP3.

DETAILED DESCRIPTION Definitions

A “vector” as used herein refers to a macromolecule or association of macromolecules that comprises or associates with a polynucleotide and which can be used to mediate delivery of the polynucleotide to a cell, either in vitro or in vivo. Illustrative vectors include, for example, plasmids, viral vectors, liposomes and other gene delivery vehicles. The polynucleotide to be delivered, sometimes referred to as a “target polynucleotide” or “transgene,” may comprise a coding sequence of interest in gene therapy (such as a gene encoding a protein of therapeutic or interest), a coding sequence of interest in vaccine development (such as a polynucleotide expressing a protein, polypeptide or peptide suitable for eliciting an immune response in a mammal), and/or a selectable or detectable marker.

“AAV” is adeno-associated virus, and may be used to refer to the naturally occurring wild-type virus itself or derivatives thereof. The term covers all subtypes, serotypes and pseudotypes, and both naturally occurring and recombinant forms, except where required otherwise. As used herein, the term “serotype” refers to an AAV which is identified by and distinguished from other AAVs based on capsid protein reactivity with defined antisera, e.g., there are nine serotypes of primate AAVs, AAV-1 to AAV-9, although there are many related AAVs. For example, serotype AAV2 is used to refer to an AAV which contains capsid proteins encoded from the cap gene of AAV 2 and a genome containing 5′ and 3′ ITR sequences from the same AAV2 serotype. For each example illustrated herein the description of the vector design and production describes the serotype of the capsid and 5′-3′ ITR sequences. The abbreviation “rAAV” refers to recombinant adeno-associated virus, also referred to as a recombinant AAV vector (or “rAAV vector”). Any AAV may be employed in the production of chimeras, including both human and nonhuman primate AAVs.

BoV is bocavirus, and may be used to refer to the naturally occurring wild-type virus itself or derivatives thereof. The term covers all subtypes, serotypes and pseudotypes, and both naturally occurring and recombinant forms, except where required otherwise. As used herein, the term “serotype” refers to a BoV, which is identified by and distinguished from other BoVs based on capsid protein reactivity with defined antisera, e.g., there are four known serotypes of human bocavirus (HBoV), HBoV1, HBoV2, HBoV3, and HBoV4. However, included in BoV are serotypes derived from other non-human mammals such as swine BoV. Uke for AAV, different serotypes of HBoV and BoV can have different tropisms that infect different cell types and organs.

rAAV/HBoV is a chimeric vector which is composed of HBoV capsids and a rAAV genome. In such a chimeric virus there is no genetic information from HBoV within the genome. The rAAV genome may be from any serotype of AAV.

rAAV/BoV is a chimeric vector which is composed of a non-human BoV capsids and a rAAV genome. In such a chimeric virus there is no genetic information from BoV within the genome. The rAAV genome may be from any serotype of AAV.

Tropism as used herein, is a term referring to the ability of a particular viral serotype to productively infect cells of differing phenotypes or organs to deliver their genomic information to the nucleus.

“Transduction” or “transducing” as used herein, are terms referring to a process for the introduction of an exogenous polynucleotide, e.g., a transgene in rAAV vector, into a host cell leading to expression of the polynucleotide, e.g., the transgene in the cell. The process includes one or more of 1) endocytosis of the chimeric virus, 2) escape from endosomes or other intracellular compartments In the cytosol of a cell, 3) trafficking of the viral particle or viral genome to the nucleus, 4) uncoating of the virus particles, and generation of expressible double stranded AAV genome forms, including circular intermediates. The rAAV expressible double stranded form may persist as a nuclear episome or optionally may integrate into the host genome. The alteration of any or a combination of endocytosis of the chimeric virus after it has bound to a cell surface receptor, escape from endosomes or other intracellular compartments to the cytosol of a cell, trafficking of the viral particle or viral genome to the nucleus, or uncoating of the virus particles, and generation of expressive double stranded AAV genome forms, including circular intermediates, by an agent of the invention, e.g., a proteasome inhibitor, may result In altered expression levels or persistence of expression, or altered trafficking to the nucleus, or altered types or relative numbers of host cells or a population of cells expressing the introduced polynucleotide. Altered expression or persistence of a polynucleotide introduced via the chimeric virus can be determined by methods well known to the art including, but not limited to, protein expression, e.g., by ELISA, flow cytometry and Western blot, measurement of and DNA and RNA production by hybridization assays, e.g., Northern blots, Southern blots and gel shift mobility assays. The agents of the invention may alter, enhance or increase viral endocytosis, escape from endosomes or other intracellular cytosolic compartments, and trafficking into or to the nucleus, uncoating of the viral particles in the nucleus, and/or increasing concatemerization or generation of double stranded expressible forms of the rAAV genome in the nucleus, so as to alter expression of the introduced polynucleotide, e.g., a transgene in a rAAV vector, in vitro or In vivo. Methods used for the introduction of the exogenous polynucleotide include well-known techniques such as transfection, lipofection, viral infection, transformation, and electroporation, as well as non-viral gene delivery techniques. The introduced polynucleotide may be stably or transiently maintained in the host cell.

“Gene delivery” refers to the introduction of an exogenous polynucleotide into a cell for gene transfer, and may encompass targeting, binding, uptake, transport, localization, replicon integration and expression.

“Gene transfer” refers to the introduction of an exogenous polynucleotide into a cell which may encompass targeting, binding, uptake, transport, localization and replicon integration, but is distinct from and does not imply subsequent expression of the gene.

“Gene expression” or “expression” refers to the process of gene transcription, translation, and post-translational modification.

A “detectable marker gene” is a gene that allows cells carrying the gene to be specifically detected (e.g., distinguished from cells which do not carry the marker gene). A large variety of such marker genes are known in the art.

A “selectable marker gene” is a gene that allows cells carrying the gene to be specifically selected for or against, in the presence of a corresponding selective agent. By way of illustration, an antibiotic resistance gene can be used as a positive selectable marker gene that allows a host cell to be positively selected for in the presence of the corresponding antibiotic. A variety of positive and negative selectable markers are known in the art, some of which are described below.

An “rAAV vector” as used herein refers to an AAV vector comprising a polynucleotide sequence not of AAV origin (i.e., a polynucleotide heterologous to AAV), typically a sequence of interest for the genetic transformation of a cell. In preferred vector constructs of this invention, the heterologous polynucleotide is flanked by one or two AAV inverted terminal repeat sequences (ITRs). The term rAAV vector encompasses both rAAV vector particles and rAAV vector plasmids.

A “Chimeric virus” or “Chimeric viral particle” refers to a viral particle composed of at least one capsid protein and an encapsidated polynucleotide, which is from a different virus.

A “helper virus” for AAV refers to a virus that allows AAV (e.g., wild-type AAV) to be replicated and packaged by a mammalian cell. A variety of such helper viruses for AAV are known in the art, including adenoviruses, herpes viruses and poxviruses such as vaccinia. The adenoviruses encompass a number of different subgroups, although Adenovirus type 5 of subgroup C is most commonly used. Numerous adenoviruses of human, non-human mammalian and avian origin are known and available from depositories such as the ATCC.

An “infectious” virus or viral particle is one that comprises a polynucleotide component, which it is capable of delivering into a cell for which the viral species is trophic. The term does not necessarily imply any replication capacity of the virus.

The term “polynucleotide” refers to a polymeric form of nucleotides of any length, including deoxyribonucleotides or ribonucleotides, or analogs thereof. A polynucleotide may comprise modified nucleotides, such as methylated or capped nucleotides and nucleotide analogs, and may be interrupted by non-nucleotide components. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. The term polynucleotide, as used herein, refers interchangeably to double- and single-stranded molecules. Unless otherwise specified or required, any embodiment of the invention described herein that is a polynucleotide encompasses both the double-stranded form and each of two complementary single-stranded forms known or predicted to make up the double-stranded form.

A “transcriptional regulatory sequence” or “TRS,” as used herein, refers to a genomic region that controls the transcription of a gene or coding sequence to which it is operably linked. Transcriptional regulatory sequences of use in the present invention generally include at least one transcriptional promoter and may also include one or more enhancers and/or terminators of transcription.

“Operably linked” refers to an arrangement of two or more components, wherein the components so described are In a relationship permitting them to function in a coordinated manner. By way of illustration, a transcriptional regulatory sequence or a promoter is operably linked to a coding sequence if the TRS or promoter promotes transcription of the coding sequence. An operably linked TRS is generally joined in cis with the coding sequence, but it is not necessarily directly adjacent to it.

“Heterologous” means derived from a genotypically distinct entity from that of the rest of the entity to which it is compared. For example, a polynucleotide introduced by genetic engineering techniques into a different cell type is a heterologous polynucleotide (and, when expressed, can encode a heterologous polypeptide). Similarly, a TRS or promoter that is removed from its native coding sequence and operably linked to a different coding sequence is a heterologous TRS or promoter.

“Packaging” as used herein refers to a series of subcellular events that results in the assembly and encapsidation of a viral vector. Thus, when a suitable vector is introduced into a packaging cell line under appropriate conditions, it can be assembled into a viral particle. Functions associated with packaging of viral vectors are described herein and In the art.

A “terminator” refers to a polynucleotide sequence that tends to diminish or prevent read-through transcription (i.e., it diminishes or prevent transcription originating on one side of the terminator from continuing through to the other side of the terminator). The degree to which transcription is disrupted is typically a function of the base sequence and/or the length of the terminator sequence. In particular, as is well known in numerous molecular biological systems, particular DNA sequences, generally referred to as “transcriptional termination sequences,” are specific sequences that tend to disrupt read-through transcription by RNA polymerase, presumably by causing the RNA polymerase molecule to stop and/or disengage from the DNA being transcribed. Typical examples of such sequence-specific terminators include polyadenylation (“polyA”) sequences, e.g., SV40 polyA. In addition to or in place of such sequence-specific terminators, insertions of relatively long DNA sequences between a promoter and a coding region also tend to disrupt transcription of the coding region, generally in proportion to the length of the intervening sequence. This effect presumably arises because there is always some tendency for an RNA polymerase molecule to become disengaged from the DNA being transcribed, and increasing the length of the sequence to be traversed before reaching the coding region would generally increase the likelihood that disengagement would occur before transcription of the coding region was completed or possibly even initiated. Terminators may thus prevent transcription from only one direction (“uni-directional” terminators) or from both directions (“bi-directional” terminators), and may be comprised of sequence-specific termination sequences or sequence-non-specific terminators or both. A variety of such terminator sequences are known In the art; and illustrative uses of such sequences within the context of the present invention are provided below.

“Host cells,” “cell lines,” “cell cultures,” “packaging cell line” and other such terms denote higher eukaryotic cells, e.g., mammalian cells, such human cells, useful In the present invention. These cells can be used as recipients for recombinant vectors, viruses or other transfer polynucleotides, and include the progeny of the original cell that was transduced. It is understood that the progeny of a single cell may not necessarily be completely identical (in morphology or in genomic complement) to the original parent cell.

A “therapeutic gene,” “prophylactic gene,” “target polynucleotide,” “transgene,” “gene of interest” and the like generally refer to a gene or genes to be transferred using a vector. Typically, in the context of the present invention, such genes are located within the rAAV vector (which vector is flanked by inverted terminal repeat (ITR) regions and thus can be replicated and encapsidated into rAAV particles). Target polynucleotides can be used in this invention to generate rAAV vectors for a number of different applications. Such polynucleotides include, but are not limited to: (i) polynucleotides encoding proteins useful in other forms of gene therapy to relieve deficiencies caused by missing, defective or sub-optimal levels of a structural protein or enzyme; (ii) polynucleotides that are transcribed into anti-sense molecules; (iii) polynucleotides that are transcribed into decoys that bind transcription or translation factors; (iv) polynucleotides that encode cellular modulators such as cytokines; (v) polynucleotides that can make recipient cells susceptible to specific drugs, such as the herpes virus thymidine kinase gene; and (vi) polynucleotides for cancer therapy, such as E1A tumor suppressor genes or p53 tumor suppressor genes for the treatment of various cancers. To effect expression of the transgene in a recipient host cell, it is operably linked to a promoter, either its own or a heterologous promoter. A large number of suitable promoters are known in the art, the choice of which depends on the desired level of expression of the target polynucleotide; whether one wants constitutive expression, inducible expression, cell-specific or tissue-specific expression, etc. The rAAV vector may also contain a selectable marker.

A “gene” refers to a polynucleotide containing at least one open reading frame that is capable of encoding a particular protein after being transcribed and translated.

“Recombinant,” as applied to a polynucleotide means that the polynucleotide is the product of various combinations of cloning, restriction and/or ligation steps, and other procedures that result in a construct that is distinct from a polynucleotide found in nature. A recombinant virus is a viral particle comprising a recombinant polynucleotide. The terms respectively include replicates of the original polynucleotide construct and progeny of the original virus construct.

A “control element” or “control sequence” is a nucleotide sequence involved in an interaction of molecules that contributes to the functional regulation of a polynucleotide, including replication, duplication, transcription, splicing, translation, or degradation of the polynucleotide. The regulation may affect the frequency, speed, or specificity of the process, and may be enhancing or inhibitory in nature. Control elements known in the art include, for example, transcriptional regulatory sequences such as promoters and enhancers. A promoter is a DNA region capable under certain conditions of binding RNA polymerase and initiating transcription of a coding region usually located downstream (in the 3 direction) from the promoter. Promoters include AAV promoters, e.g., P5, P19, P40 and AAV ITR promoters, as well as heterologous (to parvovirus) promoters, e.g., a CMV promoter, a beta-actin promoter, a RSV-LTR or an ubiquitin promoter.

An “expression vector” is a vector comprising a region which encodes a polypeptide of interest, and is used for effecting the expression of the protein in an intended target cell. An expression vector also comprises control elements operatively linked to the encoding region to facilitate expression of the protein in the target. The combination of control elements and a gene or genes to which they are operably linked for expression is sometimes referred to as an “expression cassette,” a large number of which are known and available in the art or can be readily constructed from components that are available in the art.

“Genetic alteration” refers to a process wherein a genetic element is introduced into a cell other than by mitosis or meiosis. The element may be heterologous to the call, or it may be an additional copy or improved version of an element already present in the cell. Genetic alteration may be effected, for example, by transfecting a cell with a recombinant plasmid or other polynucleotide through any process known in the art, such as electroporation, calcium phosphate precipitation, or contacting with a polynucleotide-liposome complex. Genetic alteration may also be effected, for example, by transduction or infection with a DNA or RNA virus or viral vector. The genetic element may be introduced into a chromosome or mini-chromosome in the cell; but any alteration that changes the phenotype and/or genotype of the call and its progeny is included in this term.

A cell is said to be “stably” altered, transduced or transformed with a genetic sequence if the sequence is available to perform its function during extended culture of the cell in vitro. In some examples, such a cell is “inheritably” altered in that a genetic alteration is introduced which is also inheritable by progeny of the altered cell.

The terms “polypeptide” and “protein” are used interchangeably herein to refer to polymers of amino acids of any length. The terms also encompass an amino acid polymer that has been modified; for example, disulfide bond formation, glycosylation, acetylation, phosphorylation, lipidation, or conjugation with a labeling component. Polypeptides such as “CFTR” and the like, when discussed in the context of gene therapy and compositions therefor, refer to the respective intact polypeptide, or any fragment or genetically engineered derivative thereof, that retains the desired biochemical function of the intact protein. Similarly, references to CFTR, and other such genes for use in gene therapy (typically referred to as “transgenes” to be delivered to a recipient cell), include polynucleotides encoding the intact polypeptide or any fragment or genetically engineered derivative possessing the desired biochemical function.

An “isolated” plasmid, virus, or other substance refers to a preparation of the substance devoid of at least some of the other components that may also be present where the substance or a similar substance naturally occurs or is initially prepared from. Thus, for example, an isolated substance may be prepared by using a purification technique to enrich it from a source mixture. Enrichment can be measured on an absolute basis, such as weight per volume of solution, or it can be measured in relation to a second, potentially interfering substance present in the source mixture.

A preparation of AAV is said to be “substantially free” of helper virus if the ratio of infectious AAV particles to infectious helper virus particles is at least about 10²:1; e.g., at least about 10⁴:1, including at least about 10⁶:1 or at least about 10⁸:1. Preparations may also be free of equivalent amounts of helper virus proteins (i.e., proteins as would be present as a result of such a level of helper virus if the helper virus particle impurities noted above were present in disrupted form). Viral and/or cellular protein contamination can generally be observed as the presence of Coomassie blue staining bands on SDS gels (e.g., the appearance of bands other than those corresponding to the AAV capsid proteins VP1, VP2 and VP3).

“Efficiency” when used in describing viral production, replication or packaging refers to useful properties of the method: in particular, the growth rate and the number of virus particles produced per cell. “High efficiency” production indicates production of at least 100 viral particles per cell; e.g., at least about 10,000 or at least about 100,000 particles per cell, over the course of the culture period specified.

The practice of the present invention will employ, unless otherwise indicated, conventional techniques of molecular biology, virology, microbiology, recombinant DNA, and immunology, which are within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Sambrook et al., 1989; Gait, 1984; Freshney, 1987; the series Methods in Enzymology (Academic Press, Inc.); Miler et al., 1987; Weir et al., 1996; Ausubel et al., 1998; Coligan et al., 1991; Coligan et al., 1995; and Scopes 1994.

I. Chimeric Viruses

Human airway epithelial cells are highly resistant to infection by most viral vectors included the adeno-associated virus (rAAV), the most widely used gene therapy vector in clinical trials. Human Bocavirus 1 (HBoV1), an autonomous human parvovirus which is likely an etiological agent of acute respiratory tract infections (ARTI) associated with wheezing in infants and young children (Allander et al., 2007; Christensen et al., 2010: Deng et al., 2012: Don et al., 2010), efficiently infects HAE from the apical membrane, resulting in replication of progeny viruses and cytopathology (Huang et al., 2012a). Impressively, HBoV1 infection of HAE at extremely low multiplicities of infection (MOI) of 10⁻³ DNAse-resistant particles (DRP) per cell results in a productive infection (see Example 2). Recently, the full-length 5543-nt HBoV1 complete genome (including terminal palindromic sequences at both ends) was cloned, and cell culture systems for HBoV1 production have been established (Example 1). Given the high efficiency of HBoV1 Infection from the apical surface of HAE, HoBV1 was hypothesized to be suitable for engineering recombinant vectors for human airway gene therapy.

HBoV1 is a relative of AAV and other Parvoviridae family members. HBoV1 belongs to the genus Bocavirus, while AAV is in the genus Dependovirus (Tijssen et al., 2011). HBoV1 and AAV are both small single-stranded DNA viruses, but 90% of encapsidated HBoV1 genomes are of the minus strand, while for AAV, an equal ratio of plus and minus strands are encapsidated (Schildgen et al., 2012). These two viruses differ greatly in their lytic phase life cycle; AAV requires co-infection with a helper virus, while HBoV1 autonomously replicates progeny in permissive cells (Huang et al., 2012a; Dijkman et al., 2009). The HBoV1 genome size is 5543 nt, 18.5% (863 nt) larger than that of AAV2 (4679-nt), and its structural features include asymmetrical hairpins with unique palindromic sequences at 5′ (140 nt) and 3′ (200 nt) termini, which are involved in replication and encapsidation, and a single P5 promoter that transcribes all viral structural and non-structural proteins (Huang et al., 2012; Chen et al., 2010). This is in contrast to the inverted terminal repeats and multiple internal promoters found in AAV genomes. HBoV1 capsid surface topology possesses common features with other parvoviruses (icosahedral capsid), and is most closely similar to human parvovirus B19 (Gurda et al., 2010). Like the cloned AAV genome, a plasmid that encodes the HBoV1 proviral genome is infectious and can be used to produce infectious particles through transfection into HEK 293 cells without the need for helper virus co-infection.

Cross-genera pseudopackaging between Parvoviridae was first established when a rAAV genome was encapsidated into a human parvovirus B19 capsid (Ponnazhagan et al., 1998). This resultant cross-genera chimera was able to deliver the rAAV genome into human bone marrow cells that are resistant to rAAV infection (Ponnazhagan et al., 1998). One important feature of the HBoV1 virus is that its genome autonomously replicates in permissive cells, in contrast to rAAV, which is a dependent parvovirus and needs helper virus coinfection for replication.

With the success in trans-complementation for rHBoV1 vector production, a so-called replicative rHBoV1 vector was developed by retaining the coding sequences for HBoV1 rep genes but replacing the structural gene by a transgene. This type of vector can deliver a high level of therapeutic gene expression in the airway cells for the therapy such as CF, AAT deficiency, COPD, or lung cancers. Such a replicating HBoV1 vector could have high utility as a vaccine against WT HBoV1 infections.

Another vector developed was an AAV2/HBoV1 chimeric virus, which packages a rAAV2 genome into a HBoV1 capsid particle. The vector was also produced in HEK293 cells with a procedure similar for rAAV vector, but the capsid genes are substituted by HBoV1 capsids. This AAV/HBoV1 vector combines both the advantages of AAV and HBoV1 transduction biology, with less safety concerns than the rHBoV1 vector since rAAV vector genomes have been extensively studied in many pre-clinical research and clinical trials, but higher airway cell tropism than rAAV. More importantly, the large HBoV1 package capacity makes it possible to encapsidate an oversized rAAV genome up to about 5.5 kb or about 6.0 kb. The 20% greater capacity than rAAV is enough to house a strong expression cassette for effective gene expression. A rAAV genome provides advantages of persistent gene expression by the stable circular transduction intermediates and double stranded genome concatemers. Indeed, AAV/HBoV1 vectors featured more persistent transgene expression than the rHBoV1 vector. Furthermore, the rescue and replication of rAAV genomes in HEK293 cells was very efficient, so that the production yield of the AAV/HBoV1 vector was also better than an rHBoV1 vector.

Utilizing the larger packaging capacity of HBoV1, a rAAV2/HBoV1-CFTR vector was previously prepared that harbors a 5.5 kb oversized rAAV genome with a 5.2 kb CFTR expression cassette having a strong chimeric promoter that included the human CMV immediate gene enhancer and the chicken β-actin promoter (CBA promoter). That vector demonstrated about 30% restoration of CFTR-mediate chloride currents in CF HAE following apical infection. Therefore, the vector could efficiently deliver normal CFTR protein expression on the surface of the airway epithelial cells and correct the defective CFTR specific chloride transport in the CF HAE. In addition, the HBoV1 genome can encapsidate the self-complementary double stranded form of a rAAV genome of about 2.7 kb to about 2.8 kb in length, which vector can bypass genome conversion and allow for enhanced or more rapid transgene expression. The AAV/HBoV chimeric vectors could also be expanded to other therapies for other lung diseases such as alpha-antitrypsin deficiency, asthma, and lung cancer, as well as vaccination against wild-type HBoV infections in infants. However, the yields of chimeric virus produced were not suitable for gene therapy applications, in contrast to the vectors and methods described herein.

The capsids and/or genomes of the viruses of the invention may be chimeric, e.g., as a result of directed evolution (see, e.g., Li et al., 2009).

II. rAAV Vectors

Besides prophylactic or therapeutic gene products, recombinant AAV vectors and/or viruses can also comprise polynucleotides that do not encode proteins, including, e.g., polynucleotides encoding for antisense mRNA (the complement of mRNA) which can be used to block the translation of normal mRNA by forming a duplex with it, and polynucleotides that encode ribozymes (RNA catalysts). In addition selected pairs of rAAV vectors having portions of open reading frames flanked by appropriately placed splice acceptor sites and/or splice donor sites, or having transcription regulatory sequences such as a heterologous enhancer, a heterologous promoter, or a heterologous enhancer and a promoter, may be employed. See, e.g., U.S. Pat. No. 6,436,392, the disclosure of which is incorporated by reference herein. For example, a first AAV vector may include a first DNA segment comprising a 5′-inverted terminal repeat of AAV; a second DNA segment comprising a promoter operably linked to a DNA fragment comprising an exon of a gene and a splice donor site, wherein the second DNA segment does not encode a full-length polypeptide; and a third DNA segment comprising a 3′-inverted terminal repeat of AAV; and a second AAV vector comprising linked: a first DNA segment comprising a 5′-inverted terminal repeat of AAV; a second DNA segment comprising a splice acceptor site and a DNA fragment with at least one other exon which together with the DNA segment of the first AAV vector encodes a full-length polypeptide; and a third DNA segment comprising a 3′-inverted terminal repeat of AAV. In one example, a first AAV vector includes the following: a first nucleic acid segment comprising a 5′-inverted terminal repeat of AAV; a second nucleic acid segment comprising a portion of a gene which includes a transcriptional regulatory region; a third nucleic acid segment comprising a splice donor site; and a fourth nucleic acid segment comprising a 3′-inverted terminal repeat of AAV; and a second AAV vector comprising linked: a first nucleic acid segment comprising a 5′-inverted terminal repeat of AAV; a second nucleic acid segment comprising a splice acceptor site; a third nucleic acid segment comprising a portion of a gene which together with the nucleic acid segment of the first AAV vector comprises a gene comprising an open reading frame which encodes a functional polypeptide; and a fourth nucleic acid segment comprising a 3′-inverted terminal repeat of AAV. In a further example, a first AAV vector includes the following: a first nucleic acid segment comprising a 5′-Inverted terminal repeat of AAV; a second nucleic acid segment comprising a splice acceptor site; a third nucleic acid segment comprising a portion of a gene; and a fourth nucleic acid segment comprising a 3′-inverted terminal repeat of AAV; and a second composition comprising a second AAV vector comprising: a first nucleic acid segment comprising a 5′-inverted terminal repeat of AAV; a second nucleic acid segment comprising a portion of a gene which together with the nucleic acid segment above having the portion comprises a gene comprising an open reading frame which encodes a functional polypeptide, wherein the portion of the gene includes a transcriptional regulatory region; a third nucleic acid segment comprising a splice donor site; a fourth nucleic acid segment comprising a 3′-inverted terminal repeat of AAV; which vectors in a host cell yield a RNA transcript which comprises sequences from the first AAV vector linked to sequences from the second AAV vector, which sequences are positioned so that the splice donor site is 5′ to the splice acceptor site, and which transcript is spliced to a mRNA which encodes the functional protein.

Adeno-associated viruses of any serotype are suitable to prepare rAAV, since the various serotypes are functionally and structurally related, even at the genetic level (see, e.g., Blacklow, 1988; and Rose, 1974). All AAV serotypes apparently exhibit similar replication properties mediated by homologous rep genes; and al generally bear three related capsid proteins such as those expressed in AAV2. The degree of relatedness is further suggested by heteroduplex analysis which reveals extensive cross-hybridization between serotypes along the length of the genome; and the presence of analogous self-annealing segments at the termini that correspond to ITRs. The similar infectivity patterns also suggest that the replication functions in each serotype are under similar regulatory control. Among the various AAV serotypes, AAV2 is most commonly employed.

An AAV vector of the invention typically comprises a polynucleotide that is heterologous to AAV. The polynucleotide is typically of interest because of a capacity to provide a function to a target cell in the context of gene therapy, such as up- or down-regulation of the expression of a certain phenotype. Such a heterologous polynucleotide or “transgene,” generally is of sufficient length to provide the desired function or encoding sequence.

Where transcription of the heterologous polynucleotide is desired in the intended target cell, it can be operably linked to its own or to a heterologous promoter, depending for example on the desired level and/or specificity of transcription within the target cell, as is known in the art. Various types of promoters and enhancers are suitable for use in this context. Constitutive promoters provide an ongoing level of gene transcription, and may be preferred when it is desired that the therapeutic or prophylactic polynucleotide be expressed on an ongoing basis. Inducible promoters generally exhibit low activity in the absence of the inducer, and are up-regulated in the presence of the inducer. They may be preferred when expression is desired only at certain times or at certain locations, or when it is desirable to titrate the level of expression using an inducing agent. Promoters and enhancers may also be tissue-specific: that is, they exhibit their activity only in certain cell types, presumably due to gene regulatory elements found uniquely in those ceils.

Illustrative examples of promoters are the SV40 late promoter from simian virus 40, the Baculovirus polyhedron enhancer/promoter element, Herpes Simplex Virus thymidine kinase (HSV tk), the immediate early promoter from cytomegalovirus (CMV) and various retroviral promoters including LTR elements. Inducible promoters include heavy metal ion inducible promoters (such as the mouse mammary tumor virus (mMTV) promoter or various growth hormone promoters), and the promoters from T7 phage which are active in the presence of T7 RNA polymerase. By way of illustration, examples of tissue-specific promoters include various surfactin promoters (for expression in the lung), myosin promoters (for expression in muscle), and albumin promoters (for expression in the liver). A large variety of other promoters are known and generally available in the art, and the sequences of many such promoters are available in sequence databases such as the GenBank database.

Where translation is also desired in the intended target cell, the heterologous polynucleotide will preferably also comprise control elements that facilitate translation (such as a ribosome binding site or “RBS” and a polyadenylation signal). Accordingly, the heterologous polynucleotide generally comprises at least one coding region operatively linked to a suitable promoter, and may also comprise, for example, an operatively linked enhancer, ribosome binding site and poly-A signal. The heterologous polynucleotide may comprise one encoding region, or more than one encoding regions under the control of the same or different promoters. The entire unit, containing a combination of control elements and encoding region, is often referred to as an expression cassette.

The heterologous polynucleotide is integrated by recombinant techniques into or in place of the AAV genomic coding region (i.e., in place of the AAV rep and cap genes), but is generally flanked on either side by AAV inverted terminal repeat (ITR) regions. This means that an ITR appears both upstream and downstream from the coding sequence, either in direct juxtaposition, e.g., (although not necessarily) without any intervening sequence of AAV origin in order to reduce the likelihood of recombination that might regenerate a replication-competent AAV genome. However, a single ITR may be sufficient to carry out the functions normally associated with configurations comprising two ITRs (see, for example, WO 94/13788), and vector constructs with only one ITR can thus be employed in conjunction with the packaging and production methods of the present invention.

The native promoters for rep are self-regulating, and can limit the amount of AAV particles produced. The rep gene can also be operably linked to a heterologous promoter, whether rep is provided as part of the vector construct, or separately. Any heterologous promoter that is not strongly down-regulated by rep gene expression is suitable; but inducible promoters may be preferred because constitutive expression of the rep gene can have a negative impact on the host cell. A large variety of inducible promoters are known in the art; including, by way of illustration, heavy metal ion inducible promoters (such as metallothionein promoters): steroid hormone inducible promoters (such as the MMTV promoter or growth hormone promoters); and promoters such as those from T7 phage which are active in the presence of T7 RNA polymerase. One sub-class of inducible promoters are those that are induced by the helper virus that is used to complement the replication and packaging of the rAAV vector. A number of helper-virus-inducible promoters have also been described, including the adenovirus early gene promoter which is inducible by adenovirus E1A protein: the adenovirus major late promoter; the herpesvirus promoter which is inducible by herpesvirus proteins such as VP16 or 1CP4; as well as vaccinia or poxvirus inducible promoters.

Methods for identifying and testing helper-virus-inducible promoters have been described (see, e.g., WO 96/17947). Thus, methods are known in the art to determine whether or not candidate promoters are helper-virus-inducible, and whether or not they will be useful in the generation of high efficiency packaging cells. Briefly, one such method involves replacing the p5 promoter of the AAV rep gene with the putative helper-virus-inducible promoter (either known in the art or identified using well-known techniques such as linkage to promoter-less “reporter” genes). The AAV rep-cap genes (with p5 replaced), e.g., linked to a positive selectable marker such as an antibiotic resistance gene, are then stably integrated Into a suitable host cell (such as the HeLa or A549 cells exemplified below). Cells that are able to grow relatively well under selection conditions (e.g., in the presence of the antibiotic) are then tested for their ability to express the rep and cap genes upon addition of a helper virus. As an initial test for rep and/or cap expression, cells can be readily screened using immunofluorescence to detect Rep and/or Cap proteins. Confirmation of packaging capabilities and efficiencies can then be determined by functional tests for replication and packaging of incoming rAAV vectors. Using this methodology, a helper-virus-inducible promoter derived from the mouse metallothionein gene has been identified as a suitable replacement for the p5 promoter, and used for producing high titers of rAAV particles (as described in WO 96/17947).

Removal of one or more AAV genes is in any case desirable, to reduce the likelihood of generating replication-competent AAV (“RCA”). Accordingly, encoding or promoter sequences for rep, cap, or both, may be removed, since the functions provided by these genes can be provided in trans.

The resultant vector is referred to as being “defective” In these functions. In order to replicate and package the vector, the missing functions are complemented with a packaging gene, or a plurality thereof, which together encode the necessary functions for the various missing rep and/or cap gene products. The packaging genes or gene cassettes are in one embodiment not flanked by AAV ITRs and in one embodiment do not share any substantial homology with the rAAV genome. Thus, in order to minimize homologous recombination during replication between the vector sequence and separately provided packaging genes, it is desirable to avoid overlap of the two polynucleotide sequences. The level of homology and corresponding frequency of recombination increase with increasing length of homologous sequences and with their level of shared identity. The level of homology that will pose a concern in a given system can be determined theoretically and confirmed experimentally, as is known in the art. Typically, however, recombination can be substantially reduced or eliminated if the overlapping sequence is less than about a 25 nucleotide sequence if it is at least 80% identical over its entire length, or less than about a 50 nucleotide sequence if it is at least 70% identical over its entire length. Of course, even lower levels of homology are preferable since they will further reduce the likelihood of recombination. It appears that, even without any overlapping homology, there is some residual frequency of generating RCA. Even further reductions in the frequency of generating RCA (e.g., by nonhomologous recombination) can be obtained by “splitting” the replication and encapsidation functions of AAV, as described by Allen et al., WO 98/27204).

The rAAV vector construct, and the complementary packaging gene constructs can be implemented in this invention in a number of different forms. Viral particles, plasmids, and stably transformed host cells can all be used to introduce such constructs into the packaging cell, either transiently or stably.

In certain embodiments of this invention, the AAV vector and complementary packaging gene(s), if any, are provided in the form of bacterial plasmids, AAV particles, or any combination thereof. In other embodiments, either the AAV vector sequence, the packaging gene(s), or both, are provided in the form of genetically altered (preferably inheritably altered) eukaryotic cells. The development of host cells inheritably altered to express the AAV vector sequence. AAV packaging genes, or both, provides an established source of the material that is expressed at a reliable level.

A variety of different genetically altered cells can thus be used in the context of this invention. By way of illustration, a mammalian host cell may be used with at least one intact copy of a stably integrated rAAV vector. An AAV packaging plasmid comprising at least an AAV rep gene operably linked to a promoter can be used to supply replication functions (as described in U.S. Pat. No. 5,658,776). Alternatively, a stable mammalian cell line with an AAV rep gene operably linked to a promoter can be used to supply replication functions (see, e.g., Trempe et al., WO 95/13392); Burstein et al. (WO 98/23018); and Johnson et al. (U.S. Pat. No. 5,656,785). The AAV cap gene, providing the encapsidation proteins as described above, can be provided together with an AAV rep gene or separately (see, e.g., the above-referenced applications and patents as well as Allen et al. (WO 98/27204). Other combinations are possible and included within the scope of this invention.

III. Uses of Chimeric Virus

The chimeric virus produced by the methods described herein can be used for administration to an individual for purposes of gene therapy or vaccination. Suitable diseases for therapy include but are not limited to those induced by viral, bacterial, or parasitic infections, various malignancies and hyperproliferative conditions, autoimmune conditions, and congenital deficiencies.

Gene therapy can be conducted to enhance the level of expression of a particular protein either within or secreted by the cell. Vectors of this invention may be used to genetically alter cells either for gene marking, replacement of a missing or defective gene, or insertion of a therapeutic gene. Alternatively, a polynucleotide may be provided to the cell that decreases the level of expression. This may be used for the suppression of an undesirable phenotype, such as the product of a gene amplified or overexpressed during the course of a malignancy, or a gene introduced or overexpressed during the course of a microbial infection. Expression levels may be decreased by supplying a therapeutic or prophylactic polynucleotide comprising a sequence capable, for example, of forming a stable hybrid with either the target gene or RNA transcript (antisense therapy), capable of acting as a ribozyme to cleave the relevant mRNA or capable of acting as a decoy for a product of the target gene.

Vaccination can be conducted to protect cells from infection by infectious pathogens. As the traditional vaccine methods, vectors of this invention may be used to delver transgenes encoding viral, bacterial, tumor or fungal antigen and their subsequent expression in host cells. The antigens, which expose to the immune system to evoke an immune response, can be in the form of virus-like particle vaccines or subunit vaccines of virus-coding proteins. Alternatively, as the method of passive immunization, vectors of this invention might be used to deliver genes encoding neutralizing antibodies and their subsequent expression in host non-hematopoietic tissues. The vaccine-like protection against pathogen infection can be conducted through direct provision of neutralizing antibody from vector-mediated transgene expression, bypassing the reliance on the natural immune system for mounting desired humoral immune responses.

The introduction of the chimeric vectors by the methods of the present invention may involve use of any number of delivery techniques (both surgical and non-surgical) which are available and well known in the art. Such delivery techniques, for example, include vascular catheterization, cannulization, injection, inhalation, endotracheal, subcutaneous, inunction, topical, oral, percutaneous, intra-arterial, intravenous, and/or intraperitoneal administrations. Vectors can also be introduced by way of bioprostheses, including, by way of illustration, vascular grafts (PTFE and dacron), heart valves, intravascular stents, intravascular paving as well as other non-vascular prostheses. General techniques regarding delivery, frequency, composition and dosage ranges of vector solutions are within the skill of the art.

In particular, for delivery of a vector of the invention to a tissue, any physical or biological method that will introduce the vector to a host animal can be employed. Vector means both a bare recombinant vector and vector DNA packaged into viral coat proteins, as is well known for administration. Simply dissolving a chimeric or rHBoV vector in phosphate buffered saline has been demonstrated to be sufficient to provide a vehicle useful for muscle tissue expression, and there are no known restrictions on the carriers or other components that can be coadministered with the vector (although compositions that degrade DNA should be avoided in the normal manner with vectors). Pharmaceutical compositions can be prepared as injectable formulations or as topical formulations to be delivered to the muscles by transdermal transport. Numerous formulations for both intramuscular injection and transdermal transport have been previously developed and can be used in the practice of the invention. The vectors can be used with any pharmaceutically acceptable carrier for ease of administration and handling.

For purposes of intramuscular injection, solutions In an adjuvant such as sesame or peanut oil or in aqueous propylene glycol can be employed, as well as sterile aqueous solutions. Such aqueous solutions can be buffered, if desired, and the liquid diluent first rendered isotonic with saline or glucose. Solutions of the chimeric or rHBoV vector as a free acid (DNA contains acidic phosphate groups) or a pharmacologically acceptable salt can be prepared in water suitably mixed with a surfactant such as hydroxypropylcellulose. A dispersion of viral particles can also be prepared in glycerol, liquid polyethylene glycols and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms. In this connection, the sterile aqueous media employed are all readily obtainable by standard techniques well-known to those skilled in the art.

The pharmaceutical forms suitable for injectable use include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be sterile and must be fluid to the extent that easy syringability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol, liquid polyethylene glycol and the like), suitable mixtures thereof, and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of a dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal and the like. In many cases it will be preferable to include isotonic agents, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by use of agents delaying absorption, for example, aluminum monostearate and gelatin.

Sterile injectable solutions are prepared by incorporating the chimeric or rHBoV vector In the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filtered sterilization. Generally, dispersions are prepared by incorporating the sterilized active ingredient into a sterile vehicle which contains the basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the methods of preparation include but are not limited to vacuum drying and the freeze drying technique which yield a powder of the active ingredient plus any additional desired ingredient from the previously sterile-filtered solution thereof.

For purposes of topical administration, dilute sterile, aqueous solutions (usually in about 0.1% to 5% concentration), otherwise similar to the above parenteral solutions, are prepared in containers suitable for incorporation into a transdermal patch, and can include known carriers, such as pharmaceutical grade dimethylsulfoxide (DMSO).

Of Interest is the correction of the genetic defect of cystic fibrosis, by supplying a properly functioning cystic fibrosis transmembrane conductance regulator (CFTR) to the airway epithelium. Thus, the use of chimeric or rHBoV vectors encoding native CFTR protein, and mutants and fragments thereof, is envisioned.

Compositions of this invention may be used in vivo as well as ex vivo. In vivo gene therapy comprises administering the vectors of this invention directly to a subject. Pharmaceutical compositions can be supplied as liquid solutions or suspensions, as emulsions, or as solid forms suitable for dissolution or suspension In liquid prior to use. For administration into the respiratory tract, one mode of administration is by aerosol, using a composition that provides either a solid or liquid aerosol when used with an appropriate aerosolubilizer device. Another mode of administration into the respiratory tract is using a flexible fiberoptic bronchoscope to instill the vectors. Typically, the viral vectors are in a pharmaceutically suitable pyrogen-free buffer such as Ringer's balanced salt solution (pH 7.4). Although not required, pharmaceutical compositions may optionally be supplied in unit dosage form suitable for administration of a precise amount.

An effective amount of virus is administered, depending on the objectives of treatment. An effective amount may be given In single or divided doses. Where a low percentage of transduction can cure a genetic deficiency, then the objective of treatment is generally to meet or exceed this level of transduction. In some instances, this level of transduction can be achieved by transduction of only about 1 to 5% of the target cells, but is more typically 20% of the cells of the desired tissue type, usually at least about 50%, at least about 80%, at least about 95%, or at least about 99% of the cells of the desired tissue type. As a guide, the number of vector particles present in a single dose given by bronchoscopy will generally be at least about 1×10¹², e.g., about 1×10¹³, 1×10¹⁴, 1×10¹⁵ or 1×10¹⁶ particles, including both DNAse-resistant and DNAse-susceptible particles. In terms of DNAse-resistant particles (DRPs), the dose will generally be between 1×10¹² and 1×10¹⁶ particles, more generally between about 1×10¹² and 1×10¹⁵ particles. The treatment can be repeated as often as every two or three weeks, as required, although treatment once in 180 days may be sufficient.

To confirm the presence of the desired DNA sequence in the host cell, a variety of assays may be performed. Such assays include, for example, “molecular biological” assays well known to those of skill In the art, such as Southern and Northern blotting, RT-PCR and PCR; “biochemical” assays, such as detecting the presence of a polypeptide expressed from a gene present in the vector, e.g., by immunological means (immunoprecipitations, immunoaffinity columns, ELISAs and Western blots) or by any other assay useful to identify the presence and/or expression of a particular nucleic acid molecule falling within the scope of the invention.

To detect and quantitate RNA produced from introduced DNA segments, RT-PCR may be employed. In this application of PCR, it is first necessary to reverse transcribe RNA into DNA, using enzymes such as reverse transcriptase, and then through the use of conventional PCR techniques amplify the DNA. In most instances PCR techniques, while useful, will not demonstrate integrity of the RNA product. Further information about the nature of the RNA product may be obtained by Northern blotting. This technique demonstrates the presence of an RNA species and gives information about the integrity of that RNA. The presence or absence of an RNA species can also be determined using dot or slot blot Northern hybridizations. These techniques are modifications of Northern blotting and only demonstrate the presence or absence of an RNA species.

While Southern blotting and PCR may be used to detect the DNA segment in question, they do not provide information as to whether the DNA segment is being expressed. Expression may be evaluated by specifically identifying the polypeptide products of the introduced DNA sequences or evaluating the phenotypic changes brought about by the expression of the introduced DNA segment in the host cell.

Thus, the effectiveness of the genetic alteration can be monitored by several criteria, including analysis of physiological fluid samples, e.g., urine, plasma, serum, blood, cerebrospinal fluid or nasal or lung washes. Samples removed by biopsy or surgical excision may be analyzed by in situ hybridization, PCR amplification using vector-specific probes, RNAse protection, immunohistology, or immunofluorescent cell counting. When the vector is administered by bronchoscopy, lung function tests may be performed, and bronchial lavage may be assessed for the presence of inflammatory cytokines. The treated subject may also be monitored for clinical features, and to determine whether the cells express the function intended to be conveyed by the therapeutic or prophylactic polynucleotide.

The decision of whether to use in vivo or ex vivo therapy, and the selection of a particular composition, dose, and route of administration will depend on a number of different factors, including but not limited to features of the condition and the subject being treated. The assessment of such features and the design of an appropriate therapeutic or prophylactic regimen is ultimately the responsibility of the prescribing physician.

The foregoing description provides, inter alia, methods for generating high titer preparations of recombinant chimeric viruses or rHBoV that are substantially free of helper virus (e.g., adenovirus) and cellular proteins. It is understood that variations may be applied to these methods by those of skill in this art without departing from the spirit of this invention.

IV. Uses and Comparison of Vectors and Methods for AAV/BoV Chimera Production

CF is caused by single gene defect in the cystic fibrosis transmembrane conductance regulator (CFTR), is the most common life-threatening inherent disease with about $450 million spent annually on patient care in the U.S alone. Gene therapy appears the best cure to permanently treat this disorder, regardless of the gene mutation/genotype, by replacing the defective CFTR gene with a corrected gene. rAAV/BoV vector also can be applied for the gene therapy to treat other airway diseases caused by inherited gene defects such as alpha-antitrypsin (AAT) deficiency and other chronic acquired respiratory disorders such as asthma. Other applications include the treatment lung cancers and prevention of infectious diseases caused by respiratory viruses through vaccination.

Previously, a gene transfer vector, rAAV/HBoV1 for human pulmonary disease gene therapy and vaccines, was constructed (Yan et al., 2013). rAAV/HBoV1 vector is highly efficient at transduction of the human airway and has larger packaging capacity than rAAV vectors that use AAV capsid. This chimeric vector solved the problem of the lack of efficient viral vector to transduce human airway, and is of great interest in the gene therapy application for cystic fibrosis (CF) due to its larger packaging capacity. The system used a non-replicating HBoV nonstructural (NS) and capsid proteins (Cap)-expressing plasmid, pHBoV1NSCap, as the packaging helper to produce rAAV/HBoV1 vector. The production yield of purified vector is 2×10¹¹ DRP (DNAse digestion-resistant particles) per 40 (145 mm)-plates transfected HEK 293 cells, that is about 400 to 600 DRP/cell (in crude lysate) or 250 DRP/cell (purified vector), and is about 5 to 10% of the yield of rAAV2 vector production in transfected 293 cells. This production yield is sufficient for routine studies in the laboratory on vector biology and functional assays of transduction. For example, this system an AAV/HBoV vector was produced harboring a 5.5 kb oversized rAAV genome with a 5.2 kb strong CFTR expression cassette. The function and efficacy of this novel CFTR vector has been validated in cystic fibrosis (CF) polarized human airway epithelial cultures grown at an air-liquid interface (HAE-ALI). Following apical infection, the vector can efficiently deliver normal CFTR protein expression on the surface of the airway epithelial cells and correct defective CFTR chloride transport defects in CF HAE-ALI cultures (Yan et al, 2013). However, for preclinical studies in experimental animals and future clinical trial, this production yield is not sufficient.

Thus, prior to this disclosure, where an HBoV nonstructural and capsid proteins-expressing plasmid pHBoV1NSCap was used as helper to cross-genus pseudopackage rAAV genome in HBoV capsid, virus production was not sufficient enough for clinical application. The present disclosure reveals details of HBoV viral protein expression profiles and the involvement of the HBoV non-structural proteins in capsid expression and vector production. These findings are likely relevant to all HBoV serotypes from human as well as other mammalian bocoviruses (not just human HBoV1). Findings on the biological properties of HBoV that are relevant to vector development include: 1) HBoV non-structural protein NP1 plays a role in regulating HBoV capsid expression and rAAV/HBoV vector packaging; 2) knockout of the proximal polyadenylation sites ((pA)p) In Cap coding sequence compensates the NP1 protein for capsid protein expression; and 3) expression of non-structural proteins NS1, NS2, NS3 and NS4 is not essential for vector production. This disclosure also relates to a series of new packaging helpers plasmids that inactivate NS1-4 expression, the exchange of endogenous P5 promoter with the CMV IE enhancer/promoter, as well as codon optimization of the capsid protein-encoding sequence. A 5- to 75-fold increment in rAAV/HBoV production can be achieved using these helpers in HEK293 cell production system, compared to the previous helper pHBoV1NSCap. These capsid expression constructs can also be employed to the baculovirus/Insect cells production system for rAAV/HBoV vector production.

The HBoV1 genetic map, which revealed a detail transcriptional profile of the HBoV1 NS and cap genes and the viral proteins expressed from different spliced mRNAs from the pre-RNA transcribed by the native P5 promoter. (See FIGS. 1 and 11 ). While investigating the involvement of the HBoV non-structural protein on capsid protein expression, it was found that: 1) ectopic expression of the HBoV1 cap ORF is not sufficient to express capsid proteins, due to the poor production of mRNA in the cytoplasm; 2) non-structural protein NP1 is the critical component required for regulating HBoV capsid expression, which facilitates the splicing of capsid protein-encoding mRNA and thereby activates capsid expression; 3) the expression of non-structural proteins NS1, NS2, NS3 and NS4 are not essential for capsid protein expression; 4) internal polyadenylation prevents HBoV1 pre-mRNA transcription through proximal polyadenylation (pA)p sites within the capsid protein coding sequence, knockout of the (pA)p sites compensates for the requirement of NP1 protein in the expression of capsid proteins.

The utility of these findings on HBoV1 biology hinge on whether they can be used to improve the efficiency of chimeric rAAV/HBoV vector production. The ability of a new packaging system to improve chimeric rAAV/HBoV vector production was tested. Two series of HBoV1 capsid expression constructs were generated and tested for their efficiency of pseudopackaging the rAAV genome in HBoV capsid. One set of helpers was NP1 protein expression dependent. They are the revised versions based on the pHBoVNScap helper, but the expression of NS1, NS2, NS3 and NS4 gene is null and the endogenous P5 promoter is replaced with a strong human CMV IE enhancer/promoter. This set of helpers increase vector production by 6- to 12-fold with the yield of 3,000-6,000 DRP/cell (in crude lysate) or 1,500-2,500 DRP/cell (purified vector); the transduction activity of the virus was similar to that produced with the pHBoVNSCap helper. Another set of helpers was NP1 protein expression-independent. Mammalian cell expression vector pcDNA3.1 was used to express HBoV1 capsid proteins from a synthetic HBoV1 cap cDNA (optVP1U or optVP1) without other HBoV1 sequence. optVP1U and optVP1 cDNAs were constructed with a codon optimized capsid coding sequence as well as an alternative start codon to initiate VP1 translation. In addition, the proximal polyadenylation sites (pA)p in the 5′ end of capsid protein-encoding region was removed. In optVP1U cDNA, the codon optimization is restricted in the 5′ unique region of VP1 and VP2, whereas in optVP1, the codon optimization is through the entire encoding sequence of VP1. VP2 and VP3. The CMV enhancer/promoter sequence was used to express the optVP1 cDNA, and HBoV1 VP1, VP2 and VP3 expression was as efficient as the pHBoVNSCap helper and at a similar ratio of 1:1:10. 60 to 80-fold higher chimeric vector production was obtained from this set of NP1 independent helpers. The vector production yields reach 15,000 to 40,000 DRP/cell (in crude lysate) or >10,000 DRP/cell (purified vector). However, compromised transduction activity was observed. The potency of the vector produced from NP1 independent helpers is ⅙ to 1/10 of those produced from the pHBoVNSCap or NP1 dependent helpers.

In summary, an improved rAAV/HBoV1 production system was developed that had at least a 5 to 75-fold higher efficiency than the prototype system. The current production yield is good enough for us to conduct preclinical study of the rAAV/HBoV1 vector in CF ferret model. The rAAV/HBoV1 vector produced from the improved production system using the NP1-dependent helper was a cultured in polarized airway cells and in ferrets in vivo. Although the transduction activity of the vector produced from the NP1-Independent helper is compromised, its ability to package rAAV/HBoV1 vector is superiorly high: up to 10-fold more efficient than the NP1-dependent helper.

The invention will be further described by the following non-limiting example.

Example Materials and Methods Plasmid Construction

The parent plasmid pHBoV1NSCap has been used to package rAAV2/HBoV1 vector, which contains an incomplete HBoV1 genome (nt 97 to 5,395) without the intact left and right end hairpins (Yan et al., 2013). All other plasmids based on the pHBoV1NSCap were constructed as follows, and they are also diagrammed in the figures.

pHBoV1NSCap-based plasmids: pVP2 m1, pVP2m2, pVP2m3 and pVP2m4 were constructed by mutating nt 3,422-3,427 of the HBoV1 sequence, as shown in FIG. 3A, in pHBoV1NSCap.

pCMVNSCap-based plasmids: pCMVNSCap was constructed by replacing the HBoV1 P5 promoter (nt 97-281) with the human cytomegalovirus immediate early enhancer/promoter sequence (CMV) retrieved from the pcDNA3 vector (Invitrogen/Thermo Fisher Scientific Inc. Grand Island, NY) in pHBoV1NSCap. pCMVNSCapbGHpA was constructed by replacing the HBoV1 3′ untranslational region (UTR) (nt 5,168-5,395) with the bovine hormone gene polyadenylation signal (bGHpA) of the pcDNA3 in pCMVNSCap. Based on the pCMVNSCap, NS1, NP1, and both NS1 and NP1 encoding sequences were early terminated by introducing a stop codon (Huang et al., 2012), which allowed construction of pCMVNS*Cap, pCMVNS(NP*)Cap and pCMVNS*(NP*)Cap, respectively.

VP cDNA plasmids: In pCMVNSCap, nt 282-3,091 of the HBoV1 sequence were deleted to construct pCMVCap1, and moved the VP1 open reading frame (ORF) directly under the CMV promoter to construct pCMVCap2. All D1-A1, D2-A2, and D3-A3 intron sequences were deleted to construct pCMVR6cDNA. D1-A2 and D3-A3 intron sequences were removed to construct pCMVR7cDNA. D1-A3 intron sequence were removed to construct pCMVR8cDNA. These three cDNA constructs coordinate with three VP-encoding mRNA transcripts that were previously identified, R6, R7, and R8 mRNAs, which are indicated in FIG. 1A.

Intron-replaced plasmids: The erythropoietin gene (Epo) intron 4 (Yan et al., 2000) was inserted between the D1 and A3 sites to construct pCMVCap3. Based on the pCMVNS*Cap plasmid, the D3-A3 intron sequence was deleted to construct pCMVNS*(In3Δ)Cap. Based on the pCMVNS*(In3Δ)Cap, the first and second introns were changed to Epo intron 1 and 4, respectively, to construct pCMVEpoIn14(In3Δ)Cap. Additionally, all three introns in pCMVNSCap were changed to Epo introns 1, 2, and 4, respectively, to construct pCMVEpoIn124Cap.

(pA)p knockout [m(pA)p] constructs: The potentially used five polyadenylation sites (PASs) and both their upstream and downstream elements [m(pA)p], which span the coding region for the amino acids between methionines of the VP1 and VP3 ORFs, were silently mutated through a Codon Optimization algorithm at IDT (Integrated DNA Technologies, Inc., Coralville, IA) (FIG. 2 ). An optimized Kozak sequence (GTT AAG ACG) was used to express VP1, and remained the GTG codon for VP2, in order to obtain an appropriate ratio of VP1 to VP2 and to VP3. To construct pCMVNS*(NP*)m(pA)pCap and pCMVNS*(In3Δ)m(pA)pCap, the (pA)p sites in pCMVNS*(NP*)Cap and pCMVNS*(In3Δ)Cap, respectively were mutated. In the pCMVR6-8cDNA constructs, the (pA)p sites were mutated to make pCMVR6-8cDNAm(pA)p.

Other plasmids: pOpt-NP1 was constructed by inserting a codon optimized NP1 ORF, which was synthesized at IDT, into pLenti-CMV-IRES-GFP-WPRE vector (Chen et al., 2011) through XbaI and BamHI sites. pCl-mCherry-HA was constructed by inserting a C-terminal HA-tagged mCherry ORF into pCl vector (Promega, Madison, WI) through Xho I and Xba I sites. All nucleotide numbers (nt) of the HBoV1 genome refer to the full-length HBoV1 genome (GenBank accession no.: JQ923422). Constructs were verified for HBoV1 sequence and mutations by Sanger sequencing at MCLAB (South San Francisco, CA).

Cell Culture and Transfection

HEK293 cells (CRL-1573) were purchased from American Type Culture Collection (ATCC, Manassas, VA), and were cultured in Dulbecco's modified Eagle's medium (GE Healthcare Bio-Sciences, Piscataway, NJ) with 10% fetal calf serum (Sigma-Aldrich, St. Louis, MO). Cells grown in 60-mm dishes were transfected with a total of 4 μg of plasmid DNA using LipoD293 reagent (SignaGen Laboratories, Gaithersburg. MD), following the manufacturer's instructions. The pLenti-CMV-IRES-GFP-WPRE vector (Chen et al., 2011) was cotransfected into HEK293 cells to ensure the same amount of plasmid DNA was transfected for each NP1 complementation experiment. As a control for transfection, 0.4 μg of pCl-mCherry-HA plasmid DNA was cotransfected into HEK293 cells.

Western Blotting

HEK293 cells were transfected with plasmids as indicated in each figure. Cells were harvested and lysed at 2 days post-transfection. Western blotting was performed to analyze the lysates as described In Shen et al. (2015) using the specific antibodies described in each figure. Rat anti-HBoV1 VP, NP1, and NS1 C-terminus (NS1C) were produced previously (Shen et al., 2015). Anti-β-actin and anti-HA monoclonal antibodies were purchased from Sigma-Aldrich.

RNA Isolation and Analyses

RNA isolation: Cytoplasmic RNA was purified from transfected cells following the QIAGEN Supplementary Protocol using the RNeasy® Mini Kit (Qiagen, Valencia, CA). For the RNA samples used for RNA export examination, the same numbers of cells were extracted for cytoplasmic RNA and total RNA using the RNeasy Mini Kit. Other total RNA samples were prepared using Trizol Regent (Invitrogen), according to the manufacturer's instructions.

Northern blotting: Five μg of cytoplasmic or total RNA samples was separated on 1.4% denaturation agarose gel, and was visualized using ethidium bromine (EB) staining. The stained 18S ribosome RNA (rRNA) bands served as loading control. Northern blot analysis was performed as described in Sun et al. (2009), using ³²P-labeled DNA probes as diagrammed in FIG. 1B. In some gels, an RNA ladder (Invitrogen) was used as a size marker (Qiu et al., 2002).

RNAse protection assay (RPA): RPA was performed as described in Chen et al. (2010) and Sun et al. (2009). RPA probes were constructed by cloning the indicated sequence (FIG. 1B) into BamHI/HindIII-digested vector pGEM4Z (Promega). The protected bands by the indicated probe are diagrammed in FIG. 1B.

Quantification: Images of both Northern blotting and RPA were processed using a GE Typhoon FLA 9000 phosphor imager (GE Healthcare Bio-Sciences, Pittsburgh, PA). ImageQuant TL 8.1 software was used to quantify the bands on the images.

TABLE 1 rAAV2/HBoV Production from HBoV Packaging Helpers Left HBoV NS gene expression Relative Production Sequence Promoter pA (pA)p NS1 NS2 NS3 NS4 NP1 Yield Prototype Helper pHBoV1NScap YES P5 (pA)d YES YES YES YES YES YES 1 NP1 dependent helper pCMVNS1(−)Cap YES CMV IE (pA)d YES NO NO YES YES YES 5.3+/−1.0 pCMVHBoVNS1-3(−)cap YES CMV IE (pA)d YES NO NO NO YES YES 9.3+/−0.5 pCMVHBoVNS1-3(−)D'm YES CMV IE (pA)d YES NO NO NO NO YES 10.7+/−3.5  NP1 independent, VP1 and VP2 5′ unique region codon optimized pCMV-R7optVP1U NO CMV IE (pA)d NO NO NO NO NO NO 1.8+/−0.4 pCMV-NS1(+)NP1(−)optVP1U YES CMV IE (pA)d NO NO NO YES YES NO 11.7+/−2.9  pCMV-NS1-3(−)NP1(−)optVP1U YES CMV IE (pA)d NO NO NO NO YES NO 4.3+/−0.8 pcDNAoptVP1hyd NO CMV IE SV40 pA NO NO NO NO NO NO 9.5 NP1 independent, VP1, VP2 and VP3 codon fully optimized pCDNAoptVP1 NO CMV IE SV40 pA NO NO NO NO NO NO 63.2+/−10.5 Left HBoV Sequence: about 2.4 kb HBoV1 genome encodes the non-structural proteins P5: Endogenous Promoter in HBoV1 genome (pA)d: 3′ distal polyadenylation site in HBoV Genome (pA)p: proximal polyadenylation sites at center of HBoV genome (within coding sequence of 5′ unique sequence of VP1/VP2) CMV IE: human cytomegalovirus immediate early promoter/enhance SV40 pA: SV40 virus sequence containing polyadenylation sites Relative production yield from each helper is normalized to that production of 400-600 DRP (DNAsel digestion resistant particle)/cell in the production system using the prototype helper, pHBoV1, and this yield is set to 1.

Results

Identification of a Non-Canonical Initiation Site that Encodes a Novel Capsid Protein VP2

Previously, a band of capsid protein (VP*) was detected whose size is between VP1 and “VP2” in HBoV1-infected human airway epithelium and HBoV1 plasmid-transfected HEK293 cells (Shen et al., 2015), as well as in the purified rAAV2/HBoV1 vector (Yan et al., 2013). However, it wasn't known whether this VP* band is a cleaved protein of the VP1 or a novel capsid protein translated from a non-canonical initiation site, a GCU codon of the alanine at the amino acid (aa) 92 of the VP1 ORF, which has been previously identified in the expression of VP1 ORF in insect Sf9 cells (Cecchini et al., 2009). Therefore, this initiation site was examined in the expression of HBoV1 capsid proteins in HEK293 cells. Four mutations were made in the GUG and GCU codons in pHBoV1NSCap (FIG. 3A). Two mutants that bear mutations of the GUG codon, which encode the valine of aa 91 of the VP1 ORF, drastically decreased expression of the intermediate band between VP1 and VP3 (FIG. 3B, lanes 1&2). Thus, it was confirmed this intermediate band (VP*) of the HBoV1 capsid proteins is a novel capsid protein of VP2 initiated at the GUG codon at nt 3,422 of the HBoV1 genome.

HBoV1 VP cDNA is Intrinsically Inefficient to Generate VP-Encoding mRNA

In the rAAV2/HBoV1 vector production system, a non-replicating HBoV1 construct pHBoV1NSCap was used as a packaging plasmid (Yan et al., 2013), which expressed NS1-4 and NP1 (Shen et al., 2015), in addition to capsid proteins. To identify a simple packaging plasmid that expresses only capsid proteins, expressive HBoV1 capsid proteins was attempted ectopically with minimal HBoV1 sequence containing the VP ORFs. To this end, six VP expression plasmids under the control of CMV promoter, as outlined in FIG. 4A, were constructed, including three VP cDNA constructs of R6. R7, and R8 mRNAs (FIG. 1A), and the other three VP ORF constructs that contain various sequences of 5′UTR. Surprisingly, none of them expressed capsid proteins in transfected HEK 293 cells, as detected by Western blotting (FIG. 4B, lanes 2-7). Next, Northern blotting was performed to analyze VP-encoding mRNA in cytoplasm using a VP mRNA-specific Cap probe (FIG. 1B). Only a low abundance of the VP mRNA was detected in the cytoplasmic RNA preparations of the cells transfected with the three cDNA constructs and the pCMVCap3, which was less than about 20% of the VP mRNA generated from the control pHBoV1NSCap (FIGS. 4C&D, lanes 4-7). We detected almost no cytoplasmic VP mRNA from the cells transfected with pCMVCap1/2 (FIGS. 4C&D, lanes 2&3).

Taken together, these results revealed that ectopic expression of the HBoV1 VP ORF is not sufficient to express capsid proteins, due to the poor production of VP mRNA in the cytoplasm.

NP1 Protein Plays an Important Role in the Expression of Capsid Proteins

Next, it was investigated how the capsid proteins are expressed from pHBoV1NSCap. To explore systematically the effects of the cis-elements of the viral genome and of the viral proteins in trans on the expression of capsid proteins, five constructs were made, as shown in FIG. 5A. Exchange of either the P5 promoter with the CMV promoter or the 3′UTR to bGHpA did not affect the capsid protein in general (FIG. 5B, lanes 2&3 vs. 1). Knockout of the NS1 and NS2 expression in pCMVNSCap (Figure SD, lane 4, NS1) did not diminish the level of capsid proteins (FIG. 5B, lane 4, VP). However, when NP1 expression was knocked out by early termination of the NP1 ORF, both NP1 knockout constructs pCMVNS(NP*)Cap and pCMVNS*(NP*)Cap failed to express appreciable levels of capsid proteins (FIG. 5B, lanes 5&6). Next, the levels of the cytoplasmic VP mRNA in transfected cells were examined. Consistent with the capsid protein expression, NP1 knockout nearly abolished VP mRNA in the cytoplasm (FIG. 5C, lanes 5&6).

Collectively, these results provided evidence that HBoV1 NP1 plays a critical role in the expression of capsid proteins, which is due to the increased level of VP mRNA in cytoplasm, and that NS1 and NS2 proteins in trans and the cis sequences of the P5 promoter and the 3′UTR are not essential to capsid protein expression.

NP1 Protein Facilitates Splicing of VP mRNA at the A3 Splice Acceptor

Next, it was investigated how NP1 regulates capsid protein expression. Since splicing at the A3 splice acceptor of the three introns is prerequisite to the production of VP mRNAs (FIG. 1A), we examined the function of NP1 in the splicing at the A3 splice acceptor. When NP1 was knocked out, splicing at the A3 splice acceptor decreased by 78-fold (FIG. 6B, lanes 5 vs. 4), whereas the splicing of the first and second introns did not (FIG. 6B, lanes 2 vs. 1). Complementation of the NP1 in trans restored 67% of the mRNA spliced at the A3 splice acceptor (FIG. 6B, lane 6, and FIG. 6C). In parallel with the inefficient splicing at the A3 splice acceptor, cytoplasmic VP mRNA was not detectable (FIG. 6D, lane 2), and capsid proteins were not expressed from pCMVNS*(NP*)Cap (FIG. 6E, lane 2). However, complementation of the NP1 restored both the expressions of VP mRNA and of capsid proteins (FIGS. 6D&E, lane 3).

The undetectable level of cytoplasmic mRNA from the NP1 knockout mutant therefore was due to the inhibited production of VP mRNA in the nucleus and not due to the inefficient export of VP mRNA from the nucleus (FIG. 6F, lanes 3&4). VP mRNA was exported from the nucleus to cytoplasm efficiently (FIGS. 6F&G, lanes 1 vs. 2 and 5 vs. 6). In addition, VP mRNA was quite stable in the cells for a period of 24 hours, as determined by the RNA stability assay using actinomycin D (FIG. 6H).

Taken together, these results confirmed that NP1 is required for the splicing of HBoV1 mRNAs at the A3 splice acceptor, which determines the level of VP mRNA in the cytoplasm and, therefore, the production of capsid proteins.

NP1 Protein Activates VP mRNA Expression Independently of Splicing

To distinguish the function of NP1 in splicing and internal polyadenylation read-through of VP mRNA, three helper plasmids were constructed: 1) pCMVNS*(In3Δ)Cap, in which the third intron was removed (FIG. 7A, construct 1); 2) pCMVEpoIn14(In3Δ)Cap, in which the first and second introns were replaced with the Epo introns 1 and 4, respectively, and the third intron was also removed (FIG. 7A, construct 2); and 3) pCMVEpoIn124Cap, in which all three introns were replaced with Epo introns (FIG. 7A, construct 3). Since NP1 protein was encoded by the ORF 312 lying in the third intron sequence, all three constructs did not express NP1 (FIG. 7B, lanes 1-3). When NP1 was added back in trans, VP mRNA at approximately (about) 2.5 kb, which is likely the R6 mRNA that reads through the (pA)p site and is polyadenylated at the (pA)d site (FIG. 1A), increased by at least 5-fold (FIGS. 7C&D, VP mRNA), but the (pA)p mRNA at about 0.8 kb, which is spliced of all introns and polyadenylated at the (pA)p site, either remained unchanged or was significantly decreased (FIGS. 7C&D, (pA)p).

As controls, NP1 did not after splicing of the introns 1 and 2 of the mRNAs generated from pCMVNS*(In3Δ)Cap (FIG. 7E, lanes 2&5) or after splicing of the heterogeneous introns (Epo introns 1 and 4) of the mRNAs generated from pCMVEpoIn14*(In3Δ)Cap (FIG. 7E, lanes 3&6). It also did not alter splicing of the three heterogeneous Epo introns (Epo introns 1, 2, and 4) of the mRNAs generated from pCMVEpoIn124Cap (FIG. 7E, lanes 4 vs. 7, and 8 vs. 9).

Thus, these results strongly suggested that the role of NP1 in increasing the read through of the (pA)p site (the level of VP mRNA) is independent of splicing at the A3 splice acceptor and the intervening intron sequence. Since both the pCMVEpoIn14(In3Δ)Cap and pCMVEpoIn124Cap constructs did not contain any NS ORFs, the function of NP1 in facilitating the VP mRNA to read through the (pA)p site is also independent of NS1-4.

Furthermore, the impact of NP1 on the expression of VP mRNA from various VP cDNA constructs was evaluated. NP1 enhanced VP mRNA expression from the all VP cDNA constructs (FIG. 8B, lanes 4-6 vs. 1-3). With NP1 provided in trans, the level of VP mRNA was increased by 3.7-, 4-, and 6-fold from the expression of R6, R7, and R8 VP cDNAs, respectively (FIGS. 8B&C, lanes 1 vs. 4, 2 vs. 5 and 3 vs. 6). Again, as a control, with NP1 provided in trans, the NS1 and NP1 knockout construct pCMVNS*(NP*)Cap expressed VP mRNA (at about 2.5 kb; R6 in FIG. 1A), at a level of over 30 times more than that without NP1, whereas the level of (pA)p mRNA (at about 1.5 kb; R5s in FIG. 1A) did not significantly change (FIG. 8B, lanes 7 vs. 8, and FIG. 8C). However, the increased VP mRNAs from the cDNA constructs by the NP1 were still not sufficient to express capsid proteins (FIG. 8D, lanes 4-6). Of note, with the NP1 provided in trans, the level of (pA)p mRNA (at about 0.8 kb) generated from the cDNA constructs was not significantly changed (FIG. 8C, (pA)p mRNA). These results suggested that the increased read through VP mRNA is not due to the simple conversion of the (pA)p mRNA to VP mRNA.

Taken together, these results confirmed that NP1 protein facilitates VP mRNA to read through the (pA)p site, independent of any splicing events.

Knockout of the Polyadenylation Signals in the Center of the Viral Genome Compensates for the Requirement of NP1 Protein in the Expression of Capsid Proteins

Next, the role of the (pA)p site in the blockage of the read-through of VP mRNA and capsid protein expression was examined. First, mutations of the polyadenylation signal (PAS) AAUAAA site at nt 3,485 (Chen et al., 2010), as well as mutations of its upstream and downstream regions that often regulate polyadenylation (Zarudnaya et al., 2003; Huang et al., 2012) were made, in pCMVNS*Cap. We failed to decrease the level of (pA)p mRNA or increase the level of VP mRNA (data not shown). Since there are a series of five PASs in the middle of the genome, the VP1 start-VP3 start-encoding region, we made silent mutations of the entire VP1 start-VP3 start-encoding sequence [m(pA)p], which covers all five PASs (FIG. 2 ). The constructs that bear the m(pA)p mutation were observed to no longer generate (pA)p mRNA (FIG. 9B, (pA)p, lanes 2, 3 and 7-9), but produced much higher levels of VP mRNA (FIGS. 9B&C, VP mRNA, lanes 2, 3, and 7-9). In agreement with this finding, the m(pA)p mutation enabled capsid protein expression in the absence of NP1 from the NSCap gene constructs (FIG. 9D, lanes 2&3 vs. 10), as well as the VP cDNA constructs (FIG. 9D, lanes 7-9 vs. 4-6).

Thus, the present results confirmed that internal polyadenylation prevents HBoV1 pre-mRNA from transcribing through the (pA)p site, which controls the production of VP mRNA, and, therefore, prevents the expression of capsid proteins. Of note, VP mRNA expressed from the NSCap constructs migrated at the same position as the mRNA expressed from the R6cDNA did (FIG. 9B, lanes 1, 2 and 3 vs. 7), suggesting that R6 mRNA is the key VP mRNA.

Discussion

The NP1 protein is a unique small non-structural protein expressed only by members of the genus Bocaparvovirus among parvoviruses (Chen et al., 2010; Sun et al., 2009; Lederman et al., 1984; Qiu et al., 2007). It is required for efficient replication of Bocaparvovirus DNA (Huang et al., 2012; Sun et al., 2009). The NP1 protein shares features among members of Bocaparvovirus. Both the BPV1 and HBoV1 NP1 proteins can complement the loss of NP1 during MVC DNA replication to some extents (Sun et al., 2009). HBoV1 NP1 protein could complement some functions of the minute virus of mice (MVM) NS2 during an early phase of infection (Mihaylov et al., 2014).

In a previous study, MVC NP1 was shown to play a role in regulating capsid protein expression by facilitating VP mRNA transcript to read through the internal polyadenylation site (Sukhu et al., 2012). However, in that study, the function of the NP1 in enhancing splicing of VP mRNA at the A3 splice acceptor and in solely facilitating the read-through of the (pA)p site of VP mRNA (Sukhu et al., 2012) was not differentiated, since all VP mRNAs have to be spliced at the A3 splice acceptor (Dijkman et al., 2009; Chen et al., 2010, Sun et al., 2009). In the present study, it was demonstrated that NP1 plays a double role in controlling the production of VP mRNA. First. NP1 is critical to the splicing of the VP mRNA at the A3 splice acceptor, which is essential to generate VP mRNA. Second, NP1 facilitates viral pre-mRNA to read through the internal (pA)p site for the production of VP mRNA, independently of any splicing events. More importantly, the function of NP1 in capsid protein expression is independent of the other four non-structural proteins (NS1-4).

It was observed that when splicing is involved (from the constructs that contain introns), NP1 increased the level of VP mRNA on average to a much greater extent than in the absence of splicing (from these cDNA constructs) (FIG. 7 vs. 8). This finding suggests that splicing boosts NP1-facilitated read-through of the (pA)p site. Of note, while NP1 increases the read through transcript VP mRNA, (pA)p mRNA does not decrease significantly in most cases, suggesting that the increased read-through of transcripts (VP mRNA) is not merely a conversion of the (pA)p mRNA, but is likely an activation of transcription. Moreover, replacing the D3-A3 intron with heterogeneous Epo intron 4 destroyed the NP1 protein dependence of the splicing at the A3 splice acceptor (FIG. 7 ), suggesting that the role of NP1 in enhancing splicing of VP mRNA at the A3 splice site is dependent on the intervening sequence of the third intron. As we know, during cellular mRNA processing, RNA transcription, splicing, and polyadenylation are all coupled (Bentley, 2014). Therefore, it was speculated that NP1 may target the transcription complex, which initiates at the P5 promoter to activate transcription, enhances splicing at the A3 splice site, and prevents internal polyadenylation, since VP mRNA must be spliced at the A3 splice site and read through the (pA)p site. Therefore, the HBoV1 NP1 is the first example for a parvovirus nonstructural protein that has multiple functions in viral pre-mRNA processing.

The level of the VP mRNAs is not proportionally related to the level of capsid proteins (FIGS. 7 & 9 ). One interpretation could be that there is a minimal level of VP mRNA required for the translation of capsid proteins. However, in the cases of highly expressed VP mRNA from these (pA)p knockout constructs (FIG. 9), the higher level of VP mRNA did not express a higher level of capsid proteins. NP1 may play a role in the translation of VP mRNA. Without NP1 expression from the (pA)p knockout constructs, a higher level of VP1 mRNA is required to efficiently translate capsid proteins.

In this study, expression of the novel VP2 from a non-canonical translation initiation site (GUG) ORF was confirmed. Importantly, simple HBoV1 VP ORF constructs (pCMVR6-8cDNAm(pA)p), were identified which do not express any NS proteins (NS1-4 and NP1), express HBoV1 capsid proteins VP1, VP2, and VP3 at a level and at a ratio (VP1:VP2 and VP3) similar to that of the packaging helper plasmid pHBoV1NSCap for rAAV2/HBoV1 vector production (Yan et al., 2013). In fact, pCMVR8cDNA packaged rAAV2/HBoV1 vector at an efficiency higher than that by the pHBoV1NSCap (data not shown). Thus, the cDNAm(pA)p constructs will aid in the optimization of rAAV2/HBoV1 vector production in HEK293 cells without interference from any HBoV1 NS proteins.

In summary, to improve the packaging efficiency of the pHBoV1NSCap in HEK293 cells, the expression of the HBoV1 capsid proteins was studied. Expression of HBoV1 capsid proteins was found to be regulated by NP1, but not by NS1, NS2, NS3, and NS4. Without NP1, HBoV1 capsid protein-encoding transcripts are expressed at a low level that is not sufficient for the expression of capsid proteins.

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All publications, patents and patent applications are incorporated herein by reference. While in the foregoing specification, this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details herein may be varied considerably without departing from the basic principles of the invention. 

1. (canceled)
 2. A method of preparing a chimeric virus comprising a bocavirus VP1 capsid polypeptide and a recombinant adeno-associated (AAV) viral genome, comprising: a) isolating the chimeric virus from a host cell that: (1) expresses the bocavirus VP1 capsid polypeptide, and (2) does not express one or more of the bocavirus NS1, NS2, NS4 polypeptides, or any combination thereof.
 3. The method of claim 2, wherein the host cell expresses a bocavirus NS3 polypeptide.
 4. The method of claim 2, wherein the host cell does not express a functional bocavirus NP1 polypeptide.
 5. The method of claim 2, wherein the host cell is a mammalian cell.
 6. The method of claim 2, wherein the host cell is an insect cell.
 7. The method of claim 2, wherein the host cell comprises a rAAV genome.
 8. The method of claim 7, wherein the rAAV genome does not express the functional bocavirus NP1 polypeptide in trans.
 9. The method of claim 2, wherein the host cell does not express one or more of NS1, NS2, NS4 polypeptides, or any combination thereof.
 10. The method of claim 2, wherein the host cell expresses a bocavirus VP2 capsid polypeptide, a bocavirus VP3 capsid polypeptide, or a combination thereof.
 11. The method of claim 2, wherein the rAAV vector comprises an expression cassette encoding a heterologous gene product.
 12. The method of claim 11, wherein the gene product encodes a therapeutic protein.
 13. The method of claim 2, wherein the rAAV genome is a rAAV-2 genome.
 14. The method of claim 2, wherein the gene product is cystic fibrosis transmembrane conductance regulator, b-globin, g-globin, tyrosine hydroxylase, glucocerebrosidase, aryl sulfatase A, factor VIII, dystrophin, alpha 1-antitrypsin, surfactant protein SP-D, SP-A or SP-C, C1 inhibitor gene, C1-INH gene, SERPING gene erythropoietin, HBoV protein, influenza virus protein, RSV protein, a neutralizing antibody or an antigen binding fragment thereof, SARS virus protein, or a cytokine.
 15. The method of claim 2, wherein the bocavirus is a human bocavirus.
 16. The method of claim 2, wherein the method is independent of bocavirus NP1.
 17. The method of claim 16, wherein the bocavirus VP1 capsid polypeptide is encoded by a nucleic acid sequence comprising a silent mutation in one or more polyadenylation signals, relative to a wild type polyadenylation signal.
 18. The method of claim 2, wherein one or more of the following is stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 19. The method of claim 2, wherein one or more of the following is not stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 20. The method of claim 2, wherein none of the following are stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 21. A host cell comprising a chimeric virus, the chimeric virus comprising a bocavirus VP1 capsid polypeptide and a recombinant adeno-associated (AAV) viral genome, wherein the host cell (1) expresses the bocavirus VP1 capsid polypeptide; and (2) does not express one or more of the bocavirus NS1, NS2, NS4 polypeptides, or any combination thereof.
 22. The host cell of claim 21, wherein the host cell expresses a bocavirus NS3 polypeptide.
 23. The host cell of claim 21, wherein the host cell is a mammalian cell.
 24. The host cell of claim 21, wherein the host cell is an insect cell.
 25. The host cell of claim 21, wherein one or more of the following is stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 26. The host cell of claim 21, wherein one or more of the following is not stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 27. The host cell of claim 21, wherein none of the following are stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 28. A population of chimeric viruses, the population comprising a bocavirus VP1 capsid polypeptide and a recombinant adeno-associated (AAV) viral genome, wherein the population was isolated from a host cell capable of expressing the bocavirus VP1 capsid polypeptide; and wherein the host cell does not express one or more of bocavirus NS1, NS2, NS4 polypeptides, or any combination thereof.
 29. The host cell of claim 28, wherein the host cell expresses a bocavirus NS3 polypeptide.
 30. The population of claim 28, wherein the host cell is a mammalian cell.
 31. The population of claim 28, wherein the host cell is an insect cell.
 32. The population of claim 28, wherein one or more of the following is stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 33. The population of claim 28, wherein one or more of the following is not stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 34. The population of claim 28, wherein none of the following are stably integrated into a genome of the host cell: (1) a coding sequence encoding the bocavirus VP1 capsid polypeptide, (2) a coding sequence encoding a bocavirus NS3 polypeptide, and (3) the recombinant adeno-associated (AAV) viral genome.
 35. A preparation comprising a chimeric virus, the chimeric virus comprising a bocavirus VP1 capsid polypeptide and a recombinant adeno-associated (AAV) viral genome, wherein the chimeric virus was produced by a host cell capable of expressing the bocavirus VP1 capsid polypeptide; and wherein the host cell does not express one or more of bocavirus NS1, NS2, NS4 polypeptides, or any combination thereof.
 36. The preparation of claim 35, wherein the host cell expresses a bocavirus NS3 polypeptide.
 37. The population of claim 35, wherein the host cell is a mammalian cell.
 38. The population of claim 37, wherein the host cell is an insect cell.
 39. A method of treatment comprising: administering to a subject a chimeric virus comprising a bocavirus VP1 capsid polypeptide and a recombinant adeno-associated (AAV) viral genome, wherein the chimeric virus was isolated from a host cell that expresses the bocavirus VP1 capsid polypeptide; and wherein the host cell does not express one or more of bocavirus NS1, NS2, NS4 polypeptides, or any combination thereof.
 40. The method of claim 39, wherein the host cell expresses a bocavirus NS3 polypeptide.
 41. A method of preparing a chimeric virus comprising bocavirus capsid protein and a recombinant adeno-associated (AAV) viral genome which method is independent of bocavirus NP1, comprising: a) providing a bocavirus genome vector that when introduced to mammalian cells i) express bocavirus NS3 and NS4 but not NS1 and NS2, ii) expresses bocavirus capsid proteins VP1, VP2 and VP3, and iii) does not express a functional bocavirus NP1, wherein the coding region for the one or more of the VP1, VP2 or VP3 in the bocavirus genome vector is codon optimized; b) introducing the bocavirus genome vector and a rAAV vector having an AAV genome into mammalian cells that do not express bocavirus NP1 in trans, thereby producing bocavirus nonstructural proteins NS3 and NS4, bocavirus capsid proteins and a rAAV genome; and c) collecting chimeric rAAV/bocavirus virus. 